Gated imaging

ABSTRACT

An imaging system, including a transmission source providing pulse(s), and a gated sensor for receiving pulse reflections from objects located beyond a minimal range. The pulse and the gate timing are controlled for creating a sensitivity as a function of range, such that the amount of the energy received progressively increases with the range. Also an imaging method, including emitting pulse(s) to a target area, receiving reflections of pulses reflected from objects located beyond a minimal range, the receiving includes gating detection of the reflections, and progressively increasing the received energy of the reflections, by controlling the pulses and the timing of the gating.

CROSS-REFERENCE TO RELATED CASES

This is a continuation of International Application NumberPCT/IL2005/000085 which designates the U.S. and which itself claimspriority to and the benefit of both IL Patent Application No. 160220(filed in Israel on Feb. 4, 2004) and IL Patent Application No. 165090(filed in Israel on Nov. 8, 2004). International Application NumberPCT/IL2005/000085 was filed via the Patent Cooperation Treaty on Jan.24, 2005, and it published as International Publication Number WO2005/076037 A1 on Aug. 18, 2005. Priority to and the benefit ofInternational Application Number PCT/IL2005/000085, IL PatentApplication No. 160220, and IL Patent Application No. 165090 is herebyclaimed, and the contents of each of these three applications is herebyincorporated herein by reference.

FIELD OF THE DISCLOSED TECHNIQUE

The disclosed technique relates to optical observation systems ingeneral, and to a method and system for imaging using the principle ofgated imaging with active illumination, in particular.

BACKGROUND OF THE DISCLOSED TECHNIQUE

Target detection and identification using an imaging system thatincludes a camera is known in the art. Cameras, as known in the art, maybe mounted on a plurality of objects, for example, closed circuitstationary cameras mounted on walls, geostationary satellites, portablecameras, that may also be mounted on a tripod, and moving platforms,including vehicles. Such a camera often requires a high level ofsensitivity to light for use in poor visibility conditions. Also, a longfocal lens is commonly employed to achieve high optical magnification.In conditions of poor visibility, for example at night, the lowintensity of light reflected from a target, received by a camera used inan imaging system, results in low quality image resolution. In a case oflow quality image resolution, such a camera cannot produce an image withan adequate signal-to-noise ratio to exploit the total resolutioncapability of the camera, and to discern fine details of an imagedtarget for identification purposes. Therefore, when imaging during nightor in poor visibility conditions, such cameras require an auxiliarylight source to illuminate a target and thereby improve the quality ofthe captured image. The auxiliary light source may be a laser devicecapable of producing a light beam that is parallel to the line-of-sight(LOS) of the camera, and that illuminates the field-of-view (FOV) of thecamera or a part thereof. It is noted that television systems, ingeneral, use a similar illumination method for adequate imaging. Also,long focal lenses, in general, have a limited light collectingcapability due to their high f number. A high f number reduces thecapability of a lens to collect enough photons to generate an adequateimage, as compared to lenses with small f numbers.

An inherent problem in optical observation systems is the effectinclement weather conditions, such as humidity, haze, fog, mist, smokeand rain, have on the image produced. Particles or substances in theatmosphere may be associated with certain weather conditions. Forexample, haze results from aerosols in the air. These atmosphericparticles or substances may obstruct the area between an observationsystem and a target to be observed. A similar case may result when anobservation system operates in media other than air. For example, inunderwater observations, the scattering of water particles, or of airparticles above the water, may obstruct the area between an observationsystem and a target to be observed. In an observation system integratedwith a laser device for target illumination, the interference ofparticles or substances in the medium between a system and a target cancause backscatter of the light beam. This is especially true when anauxiliary light source is used to illuminate a target at night,particularly if the illuminating source is located near the camera. Thebackscatter of the light beam results in blinding of a camera used in anobservation system, especially if the camera has a high level ofsensitivity, like an Intensified CCD (ICCD). The blinding of the camerareduces the contrast of an imaged target relative to the background.This blinding of the camera is referred to as self-blinding because itis partly caused by the observation system itself. During nightconditions, contrast reduction significantly lowers the achievable rangeof imaging and target, or object, detection and identification, withrespect to the attainable detection and identification range in daylightconditions.

In order to reduce the influence of particles or substances between anobservation system and a target, and at night, in order to achievelonger identification ranges, the imaging sensor of a camera may need tobe synchronized with respect to the time that the reflected light fromthe light illuminated target is due to be received by photodetectorslocated on the observation system. In particular, a laser generatesshort light pulses at a certain frequency. The imaging sensor of thecamera is activated at the same frequency, but with a time delay that isrelated to the frequency. The light beam generated by the laser impingeson the target, and illuminates the target and the surrounding area. Whenthe light beam is emitted toward the target, the receiving assembly ofthe imaging sensor of the camera is deactivated. A small part of thelight is reflected from the target back towards the camera, which isactivated as this reflected light reaches the camera.

Light which reflects off of particles or substances relatively close tothe camera, in comparison to the longer distance between the camera andthe target, will reach the receiving assembly of the camera while thecamera is still deactivated. This light will therefore not be receivedby the camera and will not affect the contrast of the image. However,reflected light from the target and its nearby surroundings will reachthe camera after the camera has been switched to an “on” state, and solight reflected towards the camera from the target will be fullycollected by the camera.

The camera switches from an “off” state to an “on” state in asynchronized manner with the time required for the pulse to travel tothe target and return. After the light reflected from the target hasbeen received and stored, the camera reverts to an “off” state, and thesystem awaits transmission of the following light pulse. This cycle isrepeated at a rate established in accordance with the range from thecamera to the target, the speed of light in the observation medium, andthe inherent limitations of the laser device and the camera. Thistechnique is known as gated imaging with active illumination to minimizebackscatter.

U.S. Pat. No. 5,408,541 to Sewell entitled “Method and System forRecognizing Targets at Long Ranges”, is directed to a method and systemfor recognizing targets at ranges near or equal to ranges at which theyare initially detected. A detect sensor, such as a radar system or athermal imaging sensor, detects a target relative to a sensor platform.The detect sensor determines a set of range parameters, such as targetcoordinates from the sensor platform to the target. The detect sensortransfers the set of range parameters to a laser-aided image recognitionsensor (LAIRS). The LAIRS uses the set of range parameters to orient thesystem to the angular location of the target. A laser source illuminatesthe area associated with the range parameters with an imaging laserpulse to generate reflected energy from the target. A gated televisionsensor receives the reflected energy from the illuminated target, andhighly magnifies and images the reflected energy. The image is thenrecognized by either using an automatic target recognition system,displaying the image for operator recognition, or both.

It is noted that Sewell requires a preliminary range measurement. Beforethe laser source illuminates the target, the laser source directs a lowpower measurement laser pulse toward the target to measure the rangebetween the system and the target. The range sets a gating signal forthe gated television sensor. The gated television sensor is gated toturn on only when energy is reflected from the target. It is also notedthat the measuring line to the target of the laser ranger must beparallel, in a very accurate manner, to the LOS of the observationsystem.

It is an object of the disclosed technique to provide a novel system andmethod for gated imaging using active illumination that does not requirea preliminary range measurement. It is a further object of the disclosedtechnique to provide for target identification in the FOV of a camerafrom a minimal range.

SUMMARY OF THE DISCLOSED TECHNIQUE

In accordance with the disclosed technique, there is thus provided animaging system having a transmission source, the transmission sourceproviding at least one energy pulse. The system includes a sensor forreceiving pulse reflections of the at least one energy pulse reflectedfrom objects within a depth of a field to be imaged, the depth of fieldhaving a minimal range (R_(MIN)). The sensor is enabled to gatedetection of the pulse reflections, with a gate timing which iscontrolled such that the sensor starts to receive the pulse reflectionsafter a delay timing substantially given by the time it takes the atleast one energy pulse to reach the minimal range and completereflecting back to the sensor from the minimal range. The at least oneenergy pulse and the gate timing are controlled for creating asensitivity as a function of range for the system, such that an amountof received energy of the pulse reflections, reflected from objectslocated beyond the minimal range, progressively increases with the rangealong the depth of a field to be imaged. According to one embodiment,this is provided through synchronization between the timing of the atleast one energy pulse and the timing of the gate detection.

The at least one energy pulse and the gate timing may be controlled forcreating a sensitivity as a function of range for the system, such thatan amount of received energy of the pulse reflections, reflected fromobjects located beyond the minimal range, progressively increases withthe range along the depth of a field to be imaged. The amount ofreceived energy of the pulse reflections may increase progressivelyuntil an optimal range (R₀), be maintained detectable, be substantiallyconstant, or decrease gradually until a maximal range (R_(MAX)), or isdirectly proportional to the ranges of the objects to be imaged.

According to another aspect of the disclosed technique, the at least oneenergy pulse defines a substantial pulse width (T_(LASER)) commencing ata start time (T₀), and the delay timing is substantially given by thetime elapsing from the start time (T₀) until twice the minimal range(R_(MIN)) divided by the speed at which the at least one energy pulsetravels (v), in addition to the pulse width (T_(LASER)) according to theformula: $\frac{2 \times R_{MIN}}{v} + {T_{LASER}.}$

According to another embodiment, the at least one energy pulse defines asubstantial pulse width (T_(LASER)), a pulse pattern, a pulse shape, anda pulse energy, the sensor is enabled to gate detection of the pulsereflections, with a gating time span the sensor is activated (T_(ON)), aduration of time the sensor is deactivated (T_(OFF)), and asynchronization timing of the gating with respect to the at least oneenergy pulse, and at least one of the delay timing, the pulse width, thepulse shape, the pulse pattern, the pulse energy, the gating time spanthe sensor is activated (T_(ON)), the duration of time the sensor isdeactivated (T_(OFF)), and the synchronization timing, is determinedaccording to at least one of the depth of a field to be imaged, specificenvironmental conditions the system is used in, a speed the system ismoving at if the system is mounted on a moving platform, and specificcharacteristics of different objects expected to be found in the depthof field. The pulse width, the duration of time the sensor isdeactivated, and the gating time span the sensor is activated may definea cycle time, wherein the at least one energy pulse is provided for aduration of the pulse width, the opening of the sensor is delayed for aduration of the duration of time the sensor is deactivated, and thepulse reflections are received for a duration of the gating time spanthe sensor is activated. The determination according to at least one ofthe depth of a field, the specific environmental conditions, the speedthe system is moving at if the system is mounted on a moving platform,and the specific characteristics of different objects expected to befound in the depth of field, is preferably a dynamic determination, suchas varying in an increasing or decreasing manner over time.

Optionally, the pulse width and the gating time span are limited toreduce the sensitivity of the system to ambient light sources. Forexample, the pulse width is shortened progressively, the delay timing islengthened progressively, with the cycle time not changing.Alternatively, the gating time span is shortened progressively, thedelay timing is lengthened progressively, with the cycle time notchanging. In addition, the pulse width and the gating time span areshortened progressively, the delay timing is lengthened progressively,with the cycle time not changing.

According to another aspect, the gating of the sensor is utilized tocreate a sensitivity as a function of range for the system by changing aparameter such as changing the shape of the at least one energy pulse,changing the pattern of the at least one energy pulse, changing theenergy of the at least one energy pulse, changing a gating time span thesensor is activated (T_(ON)), changing a duration of time the sensor isdeactivated (T_(OFF)), changing a pulse width (T_(LASER)) of the atleast one energy pulse, changing the delay timing, and changing asynchronization timing between the gating and the timing of providingthe at least one energy pulse. The changing of a parameter may beutilized according to at least one of: the depth of field, specificenvironmental conditions the system is used in, a speed the system ismoving at if the system is mounted on a moving platform, andcharacteristics of different objects expected to be found in the depthof field.

Optionally, a controller for controlling the synchronization isprovided, preferably wherein at least one repetition of the cycle timeforms part of an individual video frame, and a number of the repetitionsforms an exposure number per video frame. Furthermore, preferably, acontrol mechanism for dynamically controlling and varying the exposurenumber is also provided. Mutual blinding between the system and asimilar system passing one another is optionally eliminated bystatistical solutions such as lowering the exposure number, a random orpre-defined change in the timing of the cycle time during the course ofthe individual video frame, and a change in frequency of the exposurenumber. Mutual blinding between the system and a similar system passingone another may also be eliminated by synchronic solutions such asestablishing a communication channel between the system and the similarsystem, letting each of the system and the similar system go intolistening modes from time to time in which the at least one energy pulseis not emitted for a listening period. After the listening period, anyof the system and the similar system resumes emitting the at least oneenergy pulse if no pulses were collected during the listening period,and after which period the system and the similar system wait until anend of a cyclic sequence before resuming emitting the at least oneenergy pulse if pulses were collected during the listening period.Furthermore, having the systems change a pulse start transmission timein the individual video frames.

The exposure number may be varied by the control mechanism according toa level of ambient light. An image intensifier may be applied, in whichcase the exposure number may be varied by the control mechanismaccording to a level of current consumed by the image intensifier. Thecontrol mechanism may include image processing means for locating areasin the sensor in a state of saturation, and image processing means forprocessing a variable number of exposures. Such image processing meansmay be utilized to take at least two video frames, one with a highexposure number, the other with a low exposure number, where theexposure numbers of the at least two video frames are determined by thecontrol mechanism. The at least two video frames are combined to form asingle video frame by combining dark areas from frames with a highexposure number and saturated areas from frames with a low exposurenumber.

According to a further feature of the invention, a pulse width(T_(LASER)) of the at least one energy pulse is substantially defined inaccordance with the following equation:${2 \times \left( \frac{R_{0} - R_{MIN}}{v} \right)},$where v is the speed at which the at least one energy pulse travels.

The at least one energy pulse may include several pulses wherein thesensor receives several pulses of the at least one energy pulsereflected from at least one object during the gating time span thesensor is activated.

The sensor may be enabled to gate detection of the pulsed reflections,with a gating time span the sensor is activated (T_(ON)), and a durationof time the sensor is deactivated (T_(OFF)), which are substantiallydefined in accordance with the following equations:$T_{ON} = {2 \times \left( \frac{R_{0} - R_{MIN}}{v} \right)}$and ${T_{OFF} = {\frac{2 \times R_{MIN}}{v} + T_{LASER}}},$where T_(LASER) is the pulse width of the at least one energy pulse, andv is the speed at which the at least one energy pulse travels.

Optionally, the sensor is enabled to gate detection of the pulsereflections in accordance with a Long Pulsed Gated Imaging (LPGI) timingtechnique. The sensor may also be enabled to gate detection of the pulsereflections with a gating time span the sensor is activated (T_(ON)),and a duration of time the sensor is deactivated (T_(OFF)), which aresubstantially defined in accordance with the following equations:$T_{ON} = {2 \times \left( \frac{R_{MAX} - R_{MIN}}{v} \right)}$and ${T_{OFF} = \frac{2 \times R_{MAX}}{v}},$where v is the speed at which the at least one energy pulse travels.

The at least one energy pulse may be in the form of electromagneticenergy or mechanical energy.

The sensor may be a Complementary Metal Oxide Semiconductor (CMOS), aCharge Coupled Device (CCD), a Gated Intensifier Charge Injection Device(GICID), a Gated Intensified CCD (GICCD), a Gated Intensified ActivePixel Sensor (GIAPS), and a Gated Image Intensifier.

The sensor may further include an external shutter, at least onephotodetector, and may also be enabled to autogate.

A display apparatus for displaying images constructed from the lightreceived in the sensor may also be used, for example, a Head Up Display(HUD) apparatus, an LCD display apparatus, a planar optic apparatus, anda holographic based flat optic apparatus.

A storage unit for storing images constructed from the pulse reflectionsreceived in the sensor may be provided, as well as a transmission devicefor transmitting images constructed from the pulse reflections receivedin the sensor.

The system may be mounted on a moving platform, and stabilized.Stabilization may preferably include stabilization using a gimbals,stabilization using feedback from a gyroscope to a gimbals,stabilization using image processing techniques, based on a spatialcorrelation between consecutively generated images of the object to beimaged, and stabilization based on sensed vibrations of the sensor.Optionally, the system includes at least one ambient light sensor.

Furthermore, a pulse detector for detection of pulses emitting from asimilar system approaching may be provided, an image-processing unit maybe added, a narrow band pass filter may be functionally connected to thesensor, and a spatial modulator shutter, or a spatial light modulator,may be provided. Optionally, an optical fiber for transmitting the atleast one energy pulse towards the objects to be imaged may be added.Furthermore, a polarizer, for filtering out incoming energy which doesnot conform to the polarization of the pulse reflection, emitted fromthe transmission source providing the at least one polarized energypulse, may be provided.

Preferably, the sensitivity of the system relates to a gain andresponsiveness of the sensor in proportion to an amount of energyreceived by the sensor, wherein the gain received by the sensor as afunction of range R is defined by the follow convolution formula:${I_{r}(R)} = \frac{\int_{T_{LASER} + T_{OFF}}^{T_{LASER} + T_{OFF} + T_{ON}}{{{L\left( {t - \frac{{2R}\quad}{v}} \right)} \cdot {C(t)}}{\mathbb{d}t}}}{T_{LASER}}$

wherein L(t) defines a Boolean function representing an on/off status ofthe transmission source, irrespective of a state of the sensor, whereL(t)=1 if the transmission source is on and L(t)=0 if the transmissionsource is off. C(t) defines a Boolean function representing an abilityof the sensor to receive incoming pulse reflections according to a stateof the sensor, where C(t)=1 if the sensor is in an activated state andC(t)=0 if the sensor is in a deactivated state, and v is the speed atwhich the at least one energy pulse travels. A value for radiantintensity may be obtained by multiplying the convolution formula by ageometrical propagation attenuation function.

The transmission device may be a laser generator, an array of diodes, anarray of LEDs, and a visible light source.

According to a further aspect of the invention, there is also providedan imaging method, including emitting at least one energy pulse to atarget area, receiving at least one reflection of the at least oneenergy pulse reflected from objects within a depth of a field to beimaged, the depth of field having a minimal range (R_(MIN)), thereceiving includes gating detection of the at least one reflection suchthat the at least one energy pulse is detected after a delay timingsubstantially given by the time it takes the at least one energy pulseto reach the minimal range and complete reflecting back, andprogressively increasing the received energy of the at least onereflection reflected from objects located beyond the minimal range alongthe depth of a field to be imaged, by controlling the at least oneenergy pulse and the timing of the gating.

Preferably, the procedure of increasing includes increasing the receivedenergy of the at least one reflection reflected from objects locatedbeyond the minimal range along the depth of a field to be imaged up toan optimal range (R₀). Furthermore, the received energy of the at leastone reflection reflected from objects located beyond the optimal rangeis maintained detectable along the depth of a field to be imaged up to amaximal range (R_(MAX)). This may be achieved by maintaining thereceived energy, of the at least one reflection reflected from objectslocated beyond the optimal range along the depth of a field to be imagedup to the maximal range, substantially constant, by gradually decreasingthe received energy, or by increasing the received energy of the atleast one reflection in direct proportion to the ranges of the objectswithin the depth of field to be imaged.

Optionally, the at least one energy pulse defines a substantial pulsewidth (T_(LASER)) commencing at a start time (T₀), and the delay timingis substantially given by the time elapsing from the start time (T₀)until twice the minimal range divided by the speed at which the at leastone energy pulse travels (v), in addition to the pulse width(T_(LASER)): $T_{LASER} + {\frac{2 \times R_{MIN}}{v}.}$Furthermore, the at least one energy pulse defines a substantial pulsewidth (T_(LASER)), a pulse pattern, a pulse shape, and a pulse energy.The procedure of gating includes a gating time span a sensor utilizedfor the receiving is activated (T_(ON)), a duration of time the sensoris deactivated (T_(OFF)), and a synchronization timing of the gatingwith respect to the at least one energy pulse. At least one of the delaytiming, the pulse width, the pulse shape, the pulse pattern, the pulseenergy, the gating time span the sensor is activated (T_(ON)), theduration of time the sensor is deactivated (T_(OFF)), and thesynchronization timing is determined according to at least one of thedepth of a field, specific environmental conditions the method is usedin, a moving speed of a moving platform if the sensor is mounted on themoving platform, and specific characteristics of different objectsexpected to be found in the depth of field.

Optionally, the method further includes the procedure of autogating.

Preferably, the procedure of controlling includes progressively changingat least one parameter such as changing a pattern of the at least oneenergy pulse, changing a shape of the at least one energy pulse,changing the energy of the at least one energy pulse, changing a gatingtime span a sensor utilized for the receiving is activated (T_(ON)),changing a duration of time the sensor is deactivated (T_(OFF)),changing an energy pulse width (T_(LASER)) of the at least one energypulse, changing the delay timing, and changing a synchronization timingbetween the gating and the emitting. The procedure of controlling mayalso include changing the at least one parameter according to at leastone of the depth of field, the specific environmental conditions themethod is used in, the moving speed of the moving platform if the sensoris mounted on the moving platform, and characteristics of differentobjects expected to be found in the depth of field. The procedure ofcontrolling may further include the sub-procedures of providing the atleast one energy pulse for a duration of the pulse width, delaying theopening of the sensor for a duration of the time the sensor isdeactivated (T_(OFF)), and receiving energy pulses reflected fromobjects for a duration of the gating time span the sensor is activated(T_(ON)). The pulse width, the duration of the time the sensor isdeactivated (T_(OFF)) and the gating time span the sensor is activated(T_(ON)) may define a cycle time. Optionally, at least one repetition ofthe cycle time may form part of an individual video frame, and a numberof repetitions may form an exposure number for the video frame.

The method may further include the procedure of eliminating mutualblinding between a system using the method and a similar system usingthe method, passing one another, by statistical solutions such aslowering the exposure number, a random or pre-defined change in thetiming of the cycle time during the course of an individual video frame,and a change in the frequency of the exposure number. Alternatively, themethod may further include the procedure of eliminating mutual blindingbetween a system using the method and a similar system using the methodpassing one another, by synchronic solutions such as establishing acommunication channel between the system and the similar system, lettingeach of the system and the similar system go into listening modes fromtime to time in which the at least one energy pulse is not emitted for alistening period. After the listening period, any of the system and thesimilar system resume emitting the at least one energy pulse if nopulses were collected during the listening period, and after whichperiod the system and the similar system wait until an end of a cyclicsequence before resuming emitting the at least one energy pulse ifpulses were collected during the listening period. Furthermore, havingthe systems change a pulse start transmission time in the individualvideo frames.

The exposure number may be dynamically varied by a control mechanism,such as by adjusting the exposure number according to a level of ambientlight, or adjusting the exposure number by the control mechanismaccording to a level of current consumed by an image intensifierutilized for intensifying the detection of the at least one reflection.Optionally, the method also includes image processing by locating areasin the sensor in a state of saturation by the control mechanism. Theimage processing may be applied for a variable number of exposures bythe control mechanism. The image processing can include taking at leasttwo video frames, one with a high exposure number, the other with a lowexposure number, by image processing of a variable number of exposures,determining exposure numbers for the at least two video frames, andcombining frames to form a single video frame by combining dark areasfrom frames with a high exposure number and saturated areas from frameswith a low exposure number. Preferably, the pulse width and the gatingtime span the sensor is activated (T_(ON)) are limited to eliminate orreduce the sensitivity of the sensor to ambient light sources.

Preferably, the procedure of increasing is dynamic, such as by varyingthe sensitivity of the sensor in a manner varying over time such as inan increasing, a decreasing, a partially increasing and a partiallydecreasing manner over time.

The procedure of controlling may include shortening the pulse widthprogressively and lengthening the delay timing progressively, whileretaining a cycle time of the gating unchanged, shortening the gatingtime span progressively and lengthening the delay timing progressively,while retaining a cycle time of the gating unchanged, or shortening thepulse width and the gating time span progressively, lengthening thedelay timing progressively, while retaining a cycle time of the gatingunchanged.

Preferably, the method includes the procedure of calculating the energypulse width (T_(LASER)), substantially defined in accordance with thefollowing equation:${2 \times \left( \frac{R_{0} - R_{MIN}}{v} \right)},$where v is the speed the at least one energy pulse travels at.

The procedure of receiving may include receiving several pulses of theat least one energy pulse reflected from objects during a gating timespan a sensor utilized for the receiving is activated (T_(ON)). Thegating may also include a duration of time the sensor is deactivated(T_(OFF)), and the controlling may include controlling the gating timespan the sensor is activated T_(ON) and a duration of time the sensor isdeactivated T_(OFF), substantially defined in accordance with thefollowing equations:$T_{ON} = {2 \times \left( \frac{R_{0} - R_{MIN}}{v} \right)}$and ${T_{OFF} = {\frac{2 \times R_{MIN}}{v} + T_{LASER}}},$where R₀ is an optimal range.

Optionally, the gating may include gating in accordance with a LongPulsed Gated Imaging (LPGI) timing technique, such as when a gating timespan a sensor utilized for the receiving is activated (T_(ON)), and aduration of time the sensor is deactivated (T_(OFF)), are substantiallydefined in accordance with the following equations:$T_{ON} = {2 \times \left( \frac{R_{MAX} - R_{MIN}}{v} \right)}$and ${T_{OFF} = \frac{2 \times R_{MAX}}{v}},$where v is the speed the at least one energy pulse travels at.

The procedure of emitting may include emitting at least one energy pulsein the form of electromagnetic energy or mechanical energy, andgenerating the at least one energy pulse by an emitter such as a lasergenerator, an array of diodes, an array of LEDs, or a visible lightsource.

The gating may include gating by a sensor, such as a Complementary MetalOxide Semiconductor (CMOS), a Charge Coupled Device (CCD), a GatedIntensifier Charge Injection Device (GICID), a Gated Intensified CCD(GICCD), and a Gated Intensified Active Pixel Sensor (GIAPS), and gatingwith a CCD sensor that includes an external shutter.

Preferably, the method further includes the procedure of intensifyingthe detection of the at least one reflection, by intensifying the atleast one reflection with a gated image intensifier or with a sensorwith shutter capabilities.

Optionally, the method also includes displaying at least one imageconstructed from the received at least one reflection. The displayingmay be on a display apparatus, for example, a Head Up Display (HUD), anLCD display, a planar optic display, and a holographic based flat opticdisplay.

Furthermore, the method also includes storing or transmitting at leastone image constructed from the received at least one reflection.

The method may also include determining the level of ambient light inthe target area, determining if other energy pulses are present in thetarget area, filtering received energy pulse reflections using a narrowband pass filter, and overcoming glare from other energy pulses bylocally darkening the entrance of an image intensifier utilized for theintensifying by using apparatuses such as a spatial modulator shutter, aspatial light modulator, or a liquid crystal display.

Optionally, the procedure of emitting includes emitting at least onepolarized electromagnetic pulse, and the procedure of receiving includesfiltering received energy according to a polarization conforming to anexpected polarization of the at least one reflection.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technique will be understood and appreciated, more fullyfrom the following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a schematic illustration of the operation of a system,constructed and operative in accordance with an embodiment of thedisclosed technique;

FIG. 2A is a schematic illustration of a laser pulse propagating throughspace;

FIG. 2B is a schematic illustration of a laser pulse propagatingtowards, and reflecting from, an object;

FIG. 3 is a graph depicting gated imaging of both a laser and a sensoras a function of time;

FIG. 4 is a typical sensitivity graph, normalized to 1, depictingsensitivity of a gated sensor as a function of the range between thesensor and a target;

FIG. 5 is a graph depicting timing adjustments relating to the pulsewidth of a laser beam, as a function of time;

FIG. 6 is a graph depicting the observation capability of a system withthe timing technique depicted in FIG. 5, as a function of range;

FIG. 7 is a graph depicting a specific instant in time in relation tothe scenario depicted in FIG. 6, as a function of range;

FIG. 8 is a graph depicting a specific instant in time after thespecific time instant depicted in FIG. 7, as a function of range;

FIG. 9 is a sensitivity graph as a function of range, normalized to 1,depicting the sensitivity of a gated sensor, in accordance with thetiming technique depicted in FIG. 5;

FIG. 10 is a sensitivity graph as a function of range, normalized to 1,depicting the sensitivity of a gated sensor, in accordance with a longpulse gated imaging timing technique;

FIG. 11 is a graph depicting the radiant intensity captured by a sensorfrom reflections from a target and from backscatter, as a function ofthe range between the sensor and the target, for both a gated and anon-gated sensor, during a simulation;

FIG. 12 is an intensity graph as a function of time, normalized to 1,depicting adjustment of the intensity shape or pattern of a laser pulse;

FIG. 13 is an intensity graph as a function of range, normalized to 1,depicting the advancement of the intensity shaped or patterned laserpulse depicted in FIG. 12;

FIG. 14 is a sensitivity graph as a function of range, normalized to 1,depicting the sensitivity of a gated sensor, in accordance with thelaser shaping technique depicted in FIG. 12;

FIG. 15 is a graph depicting the sequence of pulse cycles and thecollection of photons over an individual field, as a function of time;

FIG. 16 is a graph depicting a timing technique where a laser pulsewidth is changed dynamically over the course of obtaining an individualframe, as a function of time;

FIG. 17 is a graph depicting a timing technique where a duration that asensor unit is activated is changed dynamically over the course ofobtaining an individual frame, as a function of time;

FIG. 18 is a graph depicting a timing technique where both a laser pulsewidth and a duration that a sensor unit is activated are changeddynamically over the course of obtaining an individual frame, as afunction of time;

FIG. 19 is a graph depicting timing adjustments during the process ofobtaining an individual video field, where a total of 6666 exposures areperformed, as a function of time;

FIG. 20 is a graph depicting timing adjustments during the process ofobtaining an individual video field, where a total of 100 exposures areperformed, as a function of time;

FIG. 21 is a pair of graphs depicting timing adjustments during theprocess of obtaining an individual video field, both as a function oftime, where the number of exposures in a field is controlled based on animage processing technique;

FIG. 22 is a schematic illustration of the two image frames acquired inFIG. 21, and the combination of the two frames;

FIG. 23, which is a pair of graphs depicting a synchronization techniquefor overcoming mutual blinding, both as a function of time;

FIG. 24 is a block diagram of a method for target detection andidentification, accompanied by an illustration of a conceptual operationscenario, operative in accordance with another embodiment of thedisclosed technique;

FIG. 25 is a schematic illustration of a system, constructed andoperative in accordance with another embodiment of the disclosedtechnique; and

FIG. 26 is a schematic illustration of a system, constructed andoperative in accordance with a further embodiment of the disclosedtechnique.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed technique provides methods and systems for target orobject detection, identification and imaging, using optical observationtechniques based on the gated imaging principle with activeillumination. The disclosed technique is applicable to any kind ofimaging in any range scale, including short ranges on the order ofhundreds of meters, and also extremely short ranges, such as ranges onthe order of centimeters, millimeters and even smaller units ofmeasurement, for industrial and laboratorial applications. Accordingly,the terms “target” or “object” refer to any object in general, andalthough the disclosed technique described herein is with reference to“detection and identification”, it is equally applicable to any kind ofimage acquisition for any purpose, such as picturing, filming, acquiringvisual information, and the like. The disclosed technique describedherein is with reference to laser light pulses, however any suitablepulsed emission of electromagnetic energy radiation (photons in anyknown wavelength) may be used, including light in the visible andnon-visible spectrum, UV, near and far IR, radar, microwave, RF, gammaor other photon radiation, and the like. Also other pulsed sources ofenergy may be used, including mechanical energy such as acoustic waves,ultrasound, and the like.

Accordingly, the disclosed technique provides for manipulation of thesensitivity and image gain of a gated sensor, as a function of theimaged depth of field, by changing the width of the transmitted laserpulses, by changing the state of the sensor in a manner relating to thedistance to the target, by adjusting the number of exposures in a gatingcycle, by synchronization of the sensor to the pulse timing, and byother factors. Transmitted or emitted pulses, pulsed energy, pulsed beamand the like refer to at least one pulse, or to a beam of pulses emittedin series. The disclosed technique allows for dynamic imaging andinformation gathering in real-time. According to one embodiment, theoptical observation system is mounted on a moving platform, for example,a vehicle, such as a military aircraft. The system then provides for thedetection and identification of potential military targets in combatsituations. A vehicle is only one example of a moving platform, whereasthe latter may evidently include a non-vehicular moving platform as well(e.g. a camera dolly, or portable by a person). The disclosed techniqueis not limited to the embodiment of a moving platform, as the opticalobservation system may obviously be mounted on a stationary platform.According to another aspect of the disclosed technique, polarized lightor electromagnetic radiation is employed, thereby providing forfiltering out excessive ambient light of undesired reflections frombackground objects. Accordingly, the transmitting source emits apolarized pulse which reflects from the target objects as a polarizedpulse reflection. A polarization filter or polarizer allows into areflections sensor only incoming energy that conforms to the pulsereflections expected polarization. Most objects would reflect theoriginal polarization of the emitted pulse but some reflective objectsmay alter such polarization.

Reference is now made to FIG. 1, which is a schematic illustration ofthe operation of a system, generally referenced 100, constructed andoperative in accordance with an embodiment of the disclosed technique.

System 100 includes a laser device 102, and a sensor unit 104. Laserdevice 102 generates a laser beam 106 in the form of a single pulse or aseries of continuous pulses. Laser device 102 emits laser beam 106toward a target 108. Laser beam 106 illuminates target 108. Sensor unit104 may be a camera, or any other sensor or light collecting apparatus.

Sensor unit 104 receives reflected laser beam 110 reflected from target108. Sensor unit 104 includes at least one photodetector (not shown) forprocessing and converting received reflected light 110 into an image 112of the target. Sensor unit 104 may also include an array ofphotodetectors. Sensor unit 104 may be in one of two states. During an“on” state, sensor unit 104 receives incoming light, whereas during an“off” state sensor unit 104 does not receive incoming light. Inparticular, the shutter (not shown) of sensor unit 104 is open duringthe “on” state and closed during the “off” state. The term “activated”is used herein to refer to the sensor being in the “on” state, whereasthe term “deactivated” is used herein to refer to the sensor being inthe “off” state. Image 112 may be presented on a display, such as avideo or television display. The display may be a Head-Up Display (HUD),a Liquid Crystal Display (LCD), a display implemented with a planaroptic apparatus, a holographic based flat optic display, and the like.Image 112 may also be stored on a storage unit (not shown), ortransmitted by a transmission unit (not shown) to another location forprocessing. A controller (not shown) controls and synchronizes theoperation of sensor unit 104. It is noted that sensor unit 104 can alsobe enabled to autogate. The term autogating refers to the automaticopening and closing of the sensor shutter according to the intensity oflight received. Autogating is prevalently applied for purposes such asblocking exposure of the sensor unit to excessive light, and has nodirect connection to active transmission of pulses, their timing, ortheir gating.

Atmospheric conditions and substances, such as humidity, haze, fog,mist, smoke, rain, airborne particles, and the like, represented by zone114, exist in the surrounding area of system 100. Backscatter from thearea in the immediate proximity to system 100 has a more significantinfluence on system 100 than backscatter from a further distanced area.For example, an interfering particle relatively close to system 100 willreflect back a larger portion of beam 106 than a similar particlelocated relatively further away from system 100. Accordingly, the areaproximate to system 100 from which the avoidance of backscattered lightis desirable can be defined with an approximate range designated asR_(MIN). The target is not expected to be located within range R_(MIN),therefore the removal of the influences of atmospheric conditions orother interfering substances in this range from the captured image isdesirable. Such atmospheric conditions and substances can also bepresent beyond R_(MIN), but their removal is both problematic and oflesser significance. These atmospheric conditions and substancesinterfere with laser beam 106 on its way to illuminating target 108, andwith laser beam 110 reflected from target 108. Sensor unit 104 isdeactivated for the duration of time that laser beam 106 has completelypropagated a distance R_(MIN) toward target 108 including the returnpath to sensor unit 104 from distance R_(MIN). Range R_(MIN) is theminimum range for which sensor unit 104 is deactivated. The distancebetween system 100 and target 108 is designated range R_(MAX). It isnoted that target 108 does not need to be located at a distance of rangeR_(MAX), and can be located anywhere between range R_(MIN) and rangeR_(MAX). Range R_(MAX) represents the maximal range in which target 108is expected to be found, as the exact location of target 108 is notknown when system 100 is initially used.

In order to clearly explain how the disclosed technique provides for themanipulation of the sensitivity and image gain of a gated sensor, it isuseful to illustrate how a laser pulse propagates through space. It isalso useful to illustrate how a laser pulse propagates towards, andreflects from, an object.

Reference is now made to FIG. 2A, which is a schematic illustration of alaser pulse propagating through space. For the sake of simplicity, onlyclassical mechanics considerations are applied in the followingdescription. Laser pulse 116 emanates from laser device 115, and travelsin the direction of arrow 121. Arrow 121 points towards an increase inrange. Laser pulse 116 can be considered a train of small packets ofenergy 117, with each packet “connected” to the next, much like box carsof a real train are connected to one another. The first packet of energyof laser pulse 116 is referred to as head packet 118. The last packet ofenergy of laser pulse 116 is referred to as tail packet 119. Head packet118 is coloured black and tail packet 119 is coloured gray for purposesof clarity only. Since laser pulse 116 is made up of small packets ofenergy 117, and each packet of energy, at a particular instant, islocated at a particular point in space, then laser pulse 116 can bedescribed as having a specified length, spanning from the location wheretail packet 119 is located up to the location where head packet 118 islocated. The front part of laser pulse 116, where head packet 118 islocated, can therefore be referred to as the “head” of the laser pulse,and the back part of laser pulse 116, where tail packet 119 is located,can therefore be referred to as the “tail” of the laser pulse.Furthermore, the middle part of laser pulse 116, namely, the packetslocated between the head and the tail of the laser pulse, can bereferred to as the “body” of the laser pulse. These definitions of thehead and tail of a laser pulse will be herein referred to as such. Thelength of laser pulse 116 can also be described temporally, in terms ofhow much time laser device 115 is activated, in order to generate enoughpackets of energy, and to let the packets of energy propagate throughspace, to cover the range extended by laser pulse 116.

Reference is now made to FIG. 2B, which is a schematic illustration of alaser pulse propagating towards, and reflecting from, an object. In FIG.2B, laser pulses are emitted from laser device 122, and are received bysensor unit 124. FIG. 2B illustrates a particular instant in time whenvarious laser pulses, emitted from laser device 122 at different times,are either, propagating towards object 125, reflecting from object 125,or passing object 125. Laser pulses propagating towards, and reflectingfrom, object 125, follow trajectory 126 and its direction. For thepurposes of clarity only, the head of a laser pulse has been colouredblack, and the tail of a laser pulse has been coloured gray.

At the particular instant in time illustrated in FIG. 2B, laser pulse123A is still being generated, as only the head, and part of the body,of laser pulse 123A, has been generated. The tail, and the rest of thebody, of laser pulse 123A has not yet been generated. Laser pulse 123Apropagates in the direction of arrow 127A towards object 125. Laserpulse 123B is a full, or complete, laser pulse, which propagates in thedirection of arrow 127B towards object 125. It is noted that laser pulse123B has a head, tail and body. Laser pulse 123C has already partiallyimpinged on object 125, as the head, as well as part of the body, oflaser pulse 123C, has already impinged on object 125, and has begun toreflect back towards sensor unit 124, in the direction of arrow 127C.The tail, as well as part of the body, of laser pulse 123C, has not yetimpinged on object 125, and is therefore still propagating away fromlaser device 122. It is noted that, regarding laser pulse 123C, the headportion of the laser pulse is propagating in a direction of decreasedrange, back towards sensor unit 124, while, simultaneously, the tailportion of the laser pulse is propagating in a direction of increasedrange, away from laser device 122. Laser pulse 123D is a full, orcomplete, laser pulse, which has completely impinged upon and reflectedfrom object 125. Laser pulse 123D propagates in the direction of arrow127D towards sensor unit 124. Laser pulse 123E has already beenpartially received by sensor unit 124, as only the tail, and part of thebody, of laser pulse 123E is depicted in FIG. 2B. The head, and the restof the body, of laser pulse 123E, has already been received by sensorunit 124.

Laser pulse 123F is a full, or complete, laser pulse which did notreflect from object 125, and propagates in the direction of arrow 127F.The head, as well as part of the body, of laser pulse 123F, has alreadypassed object 125. The tail, as well as part of the body, of laser pulse123F, has not yet passed object 125. It is noted that laser pulse 123Fwas emitted at the same time laser pulse 123C was emitted. It isfurthermore noted that not all the laser pulses emitted from laserdevice 122 will reflect from the same object or location, for examplelaser pulse 123C as compared to laser pulse 123F. In general, laserdevice 122 will emit many laser pulses, in order to illuminate an area,as it is not known in advance which objects in the path of the laserpulses will reflect the laser pulses back towards a sensor unit, and howmany reflections will be received from the various ranges the laserpulses propagate through.

Reference is now made to FIG. 3, which is a graph, generally designated120, depicting gated imaging as a function of time, of both a laser anda sensor. In graph 120, a laser pulse is transmitted at time t₀. Theduration of the laser pulse, or the pulse width of the laser beam (inother words, the time the laser is on), is designated T_(LASER), andextends between time t₀ and time t₁. Between time t₁ and time t₅, thereis no transmission of a laser pulse, depicted in FIG. 3 by arrowsdemarcating a laser off time. It is noted that the description hereinrefers to a square pulse for the sake of simplicity and clarity. It isfurther noted that the description herein is equally applicable to ageneral pulse shape or pattern, in which threshold values define theeffective beginning, duration and end of the pulse, rendering itsanalysis analogous. The sensor unit is initially in the “off” state foras long as the laser pulse is emitted, between time t₀ and time t₁(T_(LASER)). The sensor unit is further maintained in the “off” statebetween time t₁ and time t₂, or during time span Δt_(MIN). The sensorunit remains in the “off” state so as not to receive reflections of theentire laser pulse (including the end portion of the pulse) from objectslocated within a range R_(MIN) from the system. As depicted in FIG. 3,T_(OFF), the time the sensor unit is in an “off” state, extends fromtime t₀ to time t₂. At time t₂, the sensor unit is activated and beginsreceiving reflections. The reflections from objects located immediatelyafter range R_(MIN) from the system are received from photons at therear end of the transmitted pulses which have impinged on these objects.The front portion of the transmitted pulses is not detected for theseobjects located immediately after range R_(MIN). At time t₃, the sensorunit first receives reflections from the entire width of the pulses. Therange of the objects, for which the entire width of the pulse is firstreceived, is designated R₀. Thus the time span between time t₂ and timet₃ is equal to T_(LASER). The sensor unit remains in the “on” stateuntil time t₅. As depicted in FIG. 3, T_(ON), the time the sensor unitis in an “on” state, extends from time t₂ to time t₅. At time t₄, thesensor unit still receives the full reflection of the pulses fromobjects located up to a range designated R₁. Reflections from objectsbeyond this range reflect progressively less portions of the laserpulse. The tail portion of the reflected pulse is cut off to a greaterextent, as the sensor shifts from its “on” state to its “off” state, thefurther away such objects are located beyond R₀ up to a maximal rangedesignated R_(MAX). R_(MAX) is the range beyond which no reflections arereceived at all, due to the deactivation of the sensor to its “off”state. At time t₅, corresponding to receiving reflections from objectsat R_(MAX) the sensor unit receives reflections only from photons at thevery front end of pulses whose tails are just about to pass range R₁.Thus the time span between time t₄ and time t₅ is equal to T_(LASER).Time span Δt_(MAX) corresponds to the time it takes a laser pulse, onceit has been fully transmitted, to reach objects located at R_(MAX).

Reference is now made to FIG. 4, which is a typical sensitivity graph,generally designated 130, depicting the sensitivity of the sensor unit,referred to in FIG. 1, as a function of the range between the sensorunit and a target area. The vertical axis represents the relativesensitivity of the sensor unit, and has been normalized to 1. Thehorizontal axis represents the range between the sensor unit and atarget. The term “sensitivity”, referred to in this context, relates tothe gain or responsiveness of the sensor unit in proportion to thenumber of reflected photons actually reaching the sensor unit when it isactive, and not to any variation in the performance of the sensor, perse. Variation in the performance of the sensor has no relation to therange from which light is reflected, if the attenuation of light, due togeometrical and atmospheric considerations, is ignored. The attenuationof light due to geometrical and atmospheric considerations is ignoredherein for the sake of simplicity. Accordingly, the amount of receivedenergy of the pulse reflections, reflected from objects located beyond aminimal range R_(MIN), progressively increases with the range along thedepth of a field to be imaged.

Range R_(MIN) is the range up to which the full reflections from atarget at this range will impinge upon sensor unit 104, referred to inFIG. 1, in a deactivated state. With reference to FIG. 3, range R_(MIN)corresponds to the time duration between time t₀ and time t₂. Range R₀is the range from which full reflections first arrive at sensor unit 104while it is activated. The reflections are the consequence of the wholespan of the pulse width passing in its entirety over a target located atrange R₀ from sensor unit 104. With reference to FIG. 3, the distancebetween range R_(MIN) and range R₀ corresponds to the time durationbetween time t₂ and time t₃. Range R₁ is the range up to which fullreflections from objects can still be obtained. With reference to FIG.3, the distance between range R₀ and range R₁ corresponds to the timeduration between time t₃ and time t₄. Range R_(MAX) is the range forwhich reflections, or any portion thereof, can still be obtained, i.e.the maximum range for which sensor sensitivity is high enough fordetection. With reference to FIG. 3, the distance between range R₁ andrange R_(MAX) corresponds to the time duration between time t₄ and timet₅. It is noted that reflections from objects located beyond R_(MAX) mayalso be received by sensor unit 104, if such targets are highlyreflective. Incoming radiation from objects located at any distance,including distances beyond R_(MAX), for example, stars, may also bereceived by sensor unit 104, if such objects emit radiation at awavelength detectable by sensor unit 104.

In graph 130, in the region ranging from range R_(MIN) up to range R₀the sensitivity of the sensor unit gradually increases to a maximumlevel of sensitivity. This region includes reflected light mainly fromatmospheric sources that cause interference and self-blinding in thesensor unit, therefore a high sensitivity is undesirable in this region.In general, the sensor unit initially encounters the photons of areflected light beam at the very front end of the transmitted laserpulse, then the photons in the middle of the pulse and finally thephotons at the very end of the pulse. In the region ranging from rangeR_(MIN) up to range R₀, the sensor doesn't detect most of the frontportion of the pulses reflected from objects just beyond R_(MIN),because of the timing of the “on” state of the sensor. In the regionranging from range R_(MIN) up to range R₀, the sensor incrementallydetects more and more of the pulse as it reflects from objects found infurther ranges. This incremental detection continues until all of thepulse is received for objects located at R₀. Thus, the duration of theincline in graph 130 is equivalent to the width of the laser pulseT_(LASER). The sensor unit remains at maximum sensitivity between rangeR₀ and range R₁. This is the region where targets are most likely to belocated, so a high sensitivity is desirable. The sensitivity of thesensor unit progressively gradually decreases to a negligible levelbeyond range R₁. In particular, for objects located immediately afterrange R₁, the sensor unit begins to not detect the photons at the veryend of the laser pulse, then for further ranges the photons in themiddle of the pulse are also not detected, and finally for objectslocated at R_(MAX), the photons at the front end of the pulse are notdetected, until no photons are received at all. The duration of thedecline in graph 130 is equivalent to the width of the laser pulseT_(LASER). It is noted that the sensitivity depicted in FIG. 4 enablessensor unit 104, and in general, system 100, referred to in FIG. 1, toobtain a level of received light energy, in system 100, which isdirectly proportional to the ranges of targets.

A particular sensitivity as a function of range may be obtained bysystem 100, referred to in FIG. 1, by the application of severaltechniques, either individually or in various combinations. Thesetechniques will now be discussed.

Reference is now made to FIG. 5, which is a graph, generally designated140, depicting timing adjustments relating to the pulse width of thelaser beam. The technique relates to the time sensor unit 104, referredto in FIG. 1, is activated with respect to the pulse width of laser beam106, referred to in FIG. 1. The vertical axis represents the status of adevice, such as a laser or a sensor unit, where ‘1’ represents a statusof a device being on, and ‘0’ represents a status of the device beingoff. The horizontal axis represents time.

Time T_(OFF) is the time during which sensor unit 104 is deactivated,immediately after transmitting laser pulse 106. Time T_(OFF) may bedetermined in accordance with the range from which reflections are notdesired (R_(MIN)), thereby preventing reflections from atmosphericconditions and substances, and the self-blinding effect. In particular,T_(OFF) may be determined as twice this range divided by the speed oflight, in the medium it is traveling in (v), as this is the time span ittakes the last photon of the laser pulse to reach the farthest point inthe range R_(MIN) and reflect back to the sensor. It may be desirable tolengthen the duration of time the sensor unit is deactivated by theduration of the pulse width of the laser beam, to ensure that nobackscattered reflections from the area up to R_(MIN) are received insensor unit 104. Therefore, T_(OFF) can be calculated using thefollowing equation: $\begin{matrix}{T_{OFF} = {\frac{2 \times R_{MIN}}{v} + T_{LASER}}} & (1)\end{matrix}$

Time T_(ON) is the time during which sensor unit 104 is activated andreceives reflections from a remote target 108, referred to in FIG. 1.Time T_(ON) may be determined in accordance with the entire distance thelast photon of a pulse that propagates up to R₀ and back to the sensorunit. Since the sensor unit is activated at time 2×R_(MIN)/v, afterlaser pulse 106 has been fully emitted, the last photon of the laserpulse is already distanced 2×R_(MIN) from the sensor unit. The lastphoton will propagate a further distance of R₀−(2×R_(MIN)) until target108, and a further distance R₀ back to the sensor, summing up to2×(R₀−R_(MIN)). The time it takes to scan this range can be calculatedby dividing the range by the speed of light, in the medium it istraveling in. Therefore, T_(ON) can be calculated using the equation:$\begin{matrix}{T_{ON} = \frac{2 \times \left( {R_{0} - R_{MIN}} \right)}{v}} & (2)\end{matrix}$

It is noted that the aforementioned calculations serve to substantiallydefine the time variables. The final values for these variables can befurther refined or customized in accordance with certain factors relatedto system 100, referred to in FIG. 1. Such refinements or customizationswill be elaborated upon hereafter, and may include, for example,accounting for specific environmental conditions, the speed of a movingplatform (if system 100 is mounted on the moving platform, such as avehicle), the specific characteristics of targets expected to be locatedat certain ranges, changing the form of laser pulse 106 and the like.

Reference is now made to FIG. 6, which is a graph, generally designated150, depicting the observation capability of a system with the timingtechnique depicted in FIG. 5. The vertical axis represents the status ofthe laser beam, where ‘1’ represents a status of the laser beam beingon, and ‘0’ represents a status of the laser beam being off. Thehorizontal axis represents distance.

Sensor unit 104, referred to in FIG. 1, is “blind” up to range R_(MIN).In particular, there are no received reflections, generated by laserpulse 106, referred to in FIG. 1, from objects located in the regionimmediately beyond system 100, referred to in FIG. 1, up to rangeR_(MIN). The range in which sensor unit 104 is “blind” is demarcated byarrows in FIG. 6 as R_(OFF). This blinding is due to the fact that laserpulse 106 propagates throughout path R_(MIN) while system 100 is blindto reflections generated by laser pulse 106 colliding with any objectthroughout this range, sensor unit 104 having been deactivated duringthis period. Thus, R_(MIN) is the minimum range for which reflections,in their entirety, may encounter sensor unit 104 in the “off” state.

Element 152 is an object to be detected, located somewhat beyond rangeR_(MIN). Element 154 is an object to be detected, located further away,slightly before range R₀. To understand how sensitivity as a function ofrange is achieved, it is helpful to examine how reflections are receivedfrom objects located at the range between R_(MIN) and R₀.

Reference is now made to FIG. 7, which is a graph, generally designated160, depicting a specific instant in time in relation to the scenariodepicted in FIG. 6. In particular, graph 160 depicts the specificinstant at which laser pulse 162 has just completed passing element 152and continues advancing. The vertical axis represents the status of thelaser beam, where ‘1’ represents a status of the laser beam being on,and ‘0’ represents a status of the laser beam being off. The horizontalaxis represents distance.

Reflections from element 152 may be received the moment sensor unit 104,referred to in FIG. 1, is activated, even before the entire pulse widthof laser pulse 162 has passed element 154. Therefore, plenty of time isprovided for sensor unit 104 to receive reflections that can beintensified from object 154, but only a limited intensifying time isprovided for reflections from the closer element 152.

Sensor unit 104 may be activated just a short time before the lastportion of pulse energy 162 is reflected from element 152, provided thatlaser beam 106, referred to in FIG. 1, remains on element 152. Thisportion is proportional to the small distance between R_(MIN) andelement 152. This portion is represented by hatched element 156. Sensorunit 104 is activated only when the tail portion, hatched element 156,of a part of laser pulse 162, reflects from element 152. Immediatelyafterwards, energy is also reflected continuously from element 154,which is being passed by advancing laser pulse 162, also in proportionto the greater distance between R_(MIN) and element 154.

Consequently, the total energy received by sensor unit 104 as aconsequence of reflections from element 152 is relative to the durationof time during which laser pulse 162 fully passes element 152, and stillmanages to reflect to a sensor unit, while the sensor unit is in the“on” state.

Reference is now made to FIG. 8, which is a graph, generally designated170, depicting a specific instant in time after the instant depicted inFIG. 7. In particular, graph 170 depicts the specific instant at whichlaser pulse 162 has just completed passing element 154 and continuesadvancing. The vertical axis represents the status of the laser beam,where ‘1’ represents a status of the laser beam being on, and ‘0’represents a status of the laser beam being off. The horizontal axisrepresents distance.

At this instant, reflections from element 154 may be received by sensorunit 104, referred to in FIG. 1, as long as laser beam 106 remainsincident on element 154. Reflections are no longer received from element152, as laser pulse 162 has already passed element 152 and anyreflections from element 152 have already passed sensor unit 104 intheir entirety. Consequently, the reflection intensity absorbed fromelement 154, located near range R₀, may be substantially greater thanthe reflection intensity absorbed from element 152. This difference inabsorbed reflection intensity is because the received reflectionintensity is determined according to the period during which sensor unit104 is activated while the element is reflecting thereto. This meansthat laser pulse 162 may remain incident on element 154 for a longertime than on element 152, during a period that sensor unit 104 isactivated, and receiving reflections. When sensor unit 104 is activated,the head and tail portions, hatched element 158, of a part of laserpulse 162, reflect from element 154. In such a case, sensor unit 104receives more energy from an object near the optimal range R₀ than froman object closer to system 100, referred to in FIG. 1, for example, anobject located slightly beyond range R_(MIN).

Reference is now made to FIG. 9, which is a sensitivity graph, generallydesignated 180, in accordance with the timing technique depicted in FIG.5, depicting the sensitivity of a gated sensor. The vertical axisrepresents relative sensitivity, and the horizontal axis representsdistance. The vertical axis has been normalized to 1.

During time T_(OFF), referred to in FIG. 5, sensor unit 104, referred toin FIG. 1, does not receive any reflections. Time T_(OFF) corresponds torange R_(MIN). At range R_(MIN), sensor unit 104 is activated. Betweenranges R_(MIN) and R₀, the sensitivity of sensor unit 104 increasesbecause increasingly more portions of laser pulse 106, referred to inFIG. 1, reflected from objects located between R_(MIN) and R₀, arereceived by sensor unit 104. Between ranges R₀ and R₁, sensor unit 104receives pulse reflections, in their entirety, from objects locatedbetween R₀ and R₁. Between ranges R₁ and R_(MAX), the sensitivity ofsensor unit 104 decreases because increasingly less portions of laserpulse 106, reflected from objects located between R₁ and R_(MAX), arereceived by sensor unit 104. At range R_(MAX), sensor unit 104 isdeactivated, and no portions of laser pulse 106 are received in sensorunit 104. Time T_(ON), referred to in FIG. 5, corresponds to thedistance between ranges R_(MIN) and R_(MAX).

It is noted that graph 180 may not be ideal, because laser pulse 106 mayalso illuminate elements, especially highly reflective elements, locatedbeyond range R_(MAX), as laser pulse 106 gradually dissipates.Furthermore, graph 180 may not be ideal because the sensitivity remainsconstant between the first optimum range R₀ and the last optimum rangeR₁, even though further attenuation exists within the range span R₁-R₀.It is possible to reduce the sensitivity of system 100, referred to inFIG. 1, for receiving reflections originating from beyond range R₀ byother techniques. Such techniques include changing the form or shape ofthe pulses of laser beam 106, changing the pattern of the pulses oflaser beam 106, changing the energy of the pulses of laser beam 106,changing the time that sensor unit 104 is activated, and changing thewidth of laser pulse 106. These techniques are now discussed.

Reference is now made to FIG. 10, which is a sensitivity graph,generally designated 184, in accordance with a Long Pulse Gated Imaging(LPGI) timing technique, depicting the sensitivity of a gated sensor.The vertical axis represents relative sensitivity, while the horizontalaxis represents distance. The vertical axis has been normalized to 1.

In the LPGI timing technique, the pulse width of the laser beam,T_(LASER) is set equal to the difference between the time required forthe laser beam to traverse the path from the system to the minimaltarget distance and back (2·R_(MIN)/v) and the time the last photonreflects back from a target located at range R₁, referred to in FIG. 9.This time is also equivalent to the duration of time for which a sensorunit is activated, T_(ON). Thus, both T_(LASER) and T_(ON) are given bythe relation: $\begin{matrix}\frac{2 \times \left( {R_{MAX} - R_{MIN}} \right)}{v} & (3)\end{matrix}$where v is the speed of light, in the medium it is traveling in. It isnoted that LPGI may be considered a particular example of the timingtechniques depicted in graphs 140, 150, 160, 170 and 180, in whichR₀=R₁. The LPGI timing technique is particularly suited for cases wherea large dynamic range, for example from 3 to 30 kilometers, needs to beimaged.

By way of an example, if a target is located at a distance of 25 km awayfrom system 100 (FIG. 1), meaning R₁ is equal to 25 km, and if R_(MIN)is equal to 3 km, and the speed of light is equal to c, the speed oflight in a vacuum, then T_(ON) and T_(LASER) will substantially equal:$\frac{2 \times \left( {{25\quad{km}} - {3\quad{km}}} \right)}{c} = {146.7\quad{{µsec}.}}$From the instant that laser beam 106, referred to in FIG. 1, istransmitted, the sensor unit operates in an LPGI mode, meaning T_(ON)will be equal in duration to T_(LASER). To eliminate backscattered lightwithout loss of contrast while maintaining a high quality image of atarget and the background, it is sufficient to switch the sensor unit tothe “off” state when the reflected beam has traversed approximately 6 km(3 km each way to and from range R_(MIN)). It is noted that it may bedesirable to lengthen time T_(OFF) by the pulse width of the laser beam,T_(LASER), to ensure that no backscattered reflections from the area upto R_(MIN) are received by the sensor unit. Therefore, the actual timeT_(OFF) is given by the following equation: $\begin{matrix}{T_{OFF} = {\frac{2 \times R_{MIN}}{v} + T_{LASER}}} & (4)\end{matrix}$In the particular case of LGPI, T_(LASER) is given by the followingequation: $\begin{matrix}{T_{LASER} = \frac{2 \times \left( {R_{MAX} - R_{MIN}} \right)}{v}} & (5)\end{matrix}$Using equations 4 and 5, T_(OFF) may be simplified to: $\begin{matrix}{T_{OFF} = {\frac{2 \times R_{MAX}}{v} + T_{LASER}}} & (6)\end{matrix}$

Reference is now made to FIG. 11, which is a graph, generally designated185, depicting the radiant intensity captured by a sensor unit fromreflections from a target and from backscatter, as a function of therange between the sensor unit and the target, for both gated andnon-gated imaging, during a simulation. Graph 185 is based on asimulation of a typical airborne system in the conditions specified atthe bottom of FIG. 11. The vertical axis represents radiant intensitylogarithmically, in units of lumens per square meter. The horizontalaxis represents range, in units of kilometers.

Curve 186 represents the radiant intensity captured by the sensor unitfrom the residual light intensity dispersed as light reflexes from thetarget, for a system operating in an LPGI mode. Curve 187 represents theradiant intensity captured by the sensor unit from backscatter as thelaser beam deflects off of atmospheric substances, for a systemoperating in an LPGI mode. Similar curves, 188 and 189, correspondingly,are provided in graph 185, for a system operating in a non-gated mode.It is noted that the form of radiant intensity curve 188 from lightreflected from the target in a non-gated mode is given, in general, bythe inverse square law of light attenuation, in vacuum, as:$\begin{matrix}\frac{1}{r^{2}} & (7)\end{matrix}$where r is the distance between the source and the target. This law isgoverned by the geometric propagation of a light beam from a source to atarget, and accounts for energy attenuation over distance. The lightbeams propagate through a mainly homogenous medium, and through anatmosphere with an aerosol density profile typical of an elevation abovesea level. It is further noted that for curves 186 and 187, bothoperating in an LPGI mode, no radiant intensity is detected up until 3km, which in FIG. 11 represents R_(MIN), the minimal range, referred toin FIG. 1.

It is noted that in an LPGI mode, the radiant intensity from backscatter(curve 187) is negligible relative to the effective radiant intensity ofthe reflection of light impinging on the surface of a target (curve186). This is the case for the entire range between 3 km and 25 km. Onthe other hand, when the system is operating in a non-gated mode, theintensity from backscatter (curve 189) is even higher than the effectiveintensity of the reflected light from the surface of the target (curve188). This is the case from the range of 2 km and over. The differencebetween target and backscatter is lower in a gated mode by up to severalorders of magnitude than in a non-gated mode, over equivalent ranges.

Therefore, it is appreciated that LPGI operation improves the contrastof the illuminated target against the backscatter light intensity forany range between 3 km and 25 km. Thus, a system operating in an LPGImode does not require knowledge of the exact range to a target. Withreference to FIG. 1, system 100 does not require knowledge of the exactrange R₀ between system 100 and target 108 (FIG. 1). A rough estimationof range R₀ is sufficient in order to calculate the required pulse widthof laser beam 106 (FIG. 1). Such an estimation can extend, in theexample of FIG. 11, between 3 to 25 km, which is particularly broad andrequires a very rough estimation in comparison to the precise rangedetermination required for modes other than the LPGI operation mode.

It is further noted that in an LPGI mode, the radiant intensity of thereflection of light from a target changes by less than a factor of tenover the 4 km to 20 km range. In contrast, in a non-gated mode, theradiant intensity of the reflection of light from the target varies by afactor of one hundred over the same range. The relative “flatness” ofcurve 186 is the result of the gradual increase of sensitivity gain of agated sensor unit, in proportion to the increase of range, representedin the graph of FIG. 10 between R_(MIN) and R₀. This gradual orprogressive increase of sensitivity is “multiplied” by the attenuationof reflected light in the inverse relation (1/r²), in vacuum,proportional to the increase in the range, represented by curve 188 inFIG. 11, resulting in the relatively “flat” curve 186. The range of 4 kmto 20 km between a sensor unit and a target is typical for manyapplications, particularly military targeting.

It is therefore appreciated that a system operating in an LPGI modeprovides effective observation (i.e. identification and detection) oftargets over a versatile depth of field. “Depth of field” refers to theranges of view confined to certain limits. With reference to FIG. 1,system 100 will produce a high quality image for both targets locatedrelatively near system 100 (beyond R_(MIN)) and targets locatedrelatively far away from system 100 (close to R₀).

The property of versatile depth of field responsiveness is highlyrelevant in the context of a television or video image having arelatively low inherent intra-scene dynamic range. This propertyprevents self-blinding and overexposure of nearby objects in the image,which occurs when using auxiliary information without the gated imagingfeature. Self-blinding and overexposure are prevented because noreflected light is observed up to the minimal range (for example,referring to FIG. 10, if R_(MIN)=3 km). Self-blinding and overexposureare also prevented because the difference in observed intensitiesbetween nearby and faraway objects is relatively small (a substantiallyflat curve for the gated target radiant intensity in graph 185).

The total irradiance Ir(R) received by a sensor unit as a function ofrange R is given by the following convolution formula: $\begin{matrix}{{I_{r}(R)} = \frac{\int_{T_{LASER} + T_{OFF}}^{T_{LASER} + T_{OFF} + T_{ON}}{{{L\left( {t - \frac{2R}{v}} \right)} \cdot {C(t)}}\quad{\mathbb{d}t}}}{T_{LASER}}} & (8)\end{matrix}$where L(t) is a Boolean function representing the existing reflection ofa laser pulse, irrespective of the on/off state of the sensor. L(t)=1 ifthe laser is “on” (i.e. the laser pulse exists over that range) andL(t)=0 if the laser is “off” (i.e. the laser pulse does not exist overthat range). C(t) is a Boolean function representing the ability of thesensor to receive incoming light according to the on/off state of thesensor. C(t)=1 if the sensor unit is in the “on” or activated state, andC(t)=0 if the senor unit is in the “off” or deactivated state.T_(LASER), T_(ON) and T_(OFF) are as they were defined above (whereT_(OFF) is the time a sensor unit has been deactivated immediatelyfollowing the completion of transmission of a laser pulse). v representsthe speed at which the laser pulse travels, in the medium in which it istraveling in.

The integral is divided by T_(LASER) to normalize the result. The valuesfor radiant intensity (e.g. the curves in graph 185) may be obtained bymultiplying the above convolution formula with a rough geometricalpropagation attenuation function of a laser pulse, such as$\frac{1}{r^{2}}$mentioned above, or a more accurate attenuation function that takes intoaccount atmospheric absorption and scattering interferences, such as${\frac{1}{r^{2}}{\mathbb{e}}^{{- 2}\gamma\quad r}},$where ‘γ’ is the atmospheric attenuation constant. The ‘γr’ in the powerof the natural exponent ‘e’ is multiplied by ‘2’ because the attenuationfunction of the laser pulse takes into account the distance covered bythe laser pulse to and from a target.

Reference is now made to FIGS. 12-14. These graphs depict a techniqueaccording to which laser pulse 106 (FIG. 1) is generated with a specificshape (of each pulse) or pattern (of pulses in a beam). Also the pulseenergy of the pulses may be varied for similar purposes. Thesetechniques illustrate the ability to change (preferably—progressively orgradually) the gradient shape of laser pulse 106 in order to achievemaximum sensitivity of system 100 (FIG. 1) at optimal range R₀. Inaccordance with graphs 150, 160 and 170, if a shaped or patterned laserpulse is generated, a substantially small number of photons of laserpulse 106 reflected from element 152 (located near system 100) and asubstantially large number of photons of laser pulse 106 reflected fromelement 154 (located remote from system 100) may be received by sensorunit 104 (FIG. 1). For example, if the form (i.e. shape or pattern) oflaser pulse 106 is selected such that the intensity is higher at the endof the pulse than at the beginning, then more light from laser pulse106, reflected from element 152, may be received in sensor unit 104,than light reflected from element 154. This would be true if the gatingof sensor unit 104 is synchronized to start receiving reflections whenthe head of a reflected pulse from R_(MIN) reaches sensor unit 104, andto stop receiving reflections when the tail of the reflected pulse fromR_(MIN) reaches sensor unit 104. For analogous purposes, the energy ofemitted pulses, and the synchronization of sensor unit 104, may beselected, such that pulses, to be reflected from objects located atgreater distances, will be received in sensor unit 104 with higherintensity (while similar shape or pattern may be retained). The pulsereflections will correspondingly cause greater energy to be received asthe reflecting objects are farther distanced, thus partially, fully, oreven excessively compensating for the energy attenuation that increaseswith the reflection distance.

FIG. 12 is a graph, generally designated 190, depicting an adjustment ofthe shape or pattern (or energy) of a laser pulse 192. The vertical axisrepresents the relative intensity of a laser pulse, and the horizontalaxis represents time. The vertical axis has been normalized to 1. TimeT_(CON) is the duration of time during which system 100 transmits laserpulse 192 at maximum intensity. Time T_(WAVE) is the duration of timeduring which the intensity of transmitted laser pulse 192 decays in ashaped or patterned manner (or by its controlled energy). T_(LASER) isthe total duration of time that laser pulse 192 is transmitted andequals T_(CON)+T_(WAVE). Time T_(OFF LASER) is the duration of timeduring which laser device 102 (FIG. 1) is in an “off” state, i.e. laserdevice 102 does not transmit anything. Time T_(OFF) is the duration oftime during which sensor unit 104 does not receive anything due to itsdeactivation. Time T_(ON) is the duration of time during which sensorunit 104 is in the “on” state and receives reflections. The timesdepicted in FIG. 12 are not proportionate, for example T_(OFF LASER) maybe much greater than T_(LASER).

FIG. 13 is a graph, generally designated 200, depicting the advancementof the shaped or patterned laser pulse depicted in FIG. 12. The verticalaxis represents the relative intensity of a laser pulse impinging uponan element, and the horizontal axis represents distance. The verticalaxis has been normalized to 1. Graph 200 depicts a specific instant intime, in particular the moment that laser pulse 192 impinges on anelement within the range R_(MIN). Reflections from the element withinrange R_(MIN) will require an additional amount of time in order toreach sensor unit 104 (FIG. 1). Sensor unit 104 will begin to collectphotons, after an additional amount of time, in accordance with theshape or pattern of laser pulse 192. Photons in range R_(MIN) exited atthe end of laser pulse 192 and were able to reach range R_(A), whensensor unit 104 is activated. Photons in range R_(WAVE) (betweendistances R_(A) and R_(B)) exited at the beginning of the intensitydecline of laser pulse 192. Photons in range R_(CON) (between distancesR_(B) and R_(C)) exited laser device 102 (FIG. 1) with maximum intensityat the beginning of the transmission of laser pulse 192.

It is appreciated that range R_(MIN) depends on time T_(OFF), whichcorresponds to the duration of time from the instance the end of laserpulse 192 reaches R_(MIN) to the instance in which the end of laserpulse 192 reflects from R_(MIN) and reaches sensor unit 104. This is theinstance at which sensor unit 104 is activated (T_(OFF)=2×R_(MIN)/v).Photons exiting at the end of laser pulse 192, which may reach sensorunit 104 after a period of time shorter than T_(OFF), may not arrivewhen sensor unit 104 is activated. Therefore, photons reflected off ofobjects located within range R_(MIN) from system 100 (FIG. 1) will notbe received by sensor unit 104 and thus, such objects will not detectedby system 100. It is further noted that relations such as 1/r² define alaser pulse shape that drops in intensity dramatically. This drop inintensity may be advantageous in terms of minimizing reflections from anelement at close range (ignoring the attenuation of laser pulse 192).

FIG. 14 is a sensitivity graph, generally designated 210, in accordancewith the laser shaping technique depicted in FIG. 12, depicting thesensitivity of a gated sensor. The vertical axis represents relativesensitivity or gain, and the horizontal axis represents distance. Thevertical axis has been normalized to 1. It is helpful to compare graph210 with graph 180 of FIG. 9, where the technique of laser shaping wasnot applied.

Accordingly, range R_(MIN) is the range from which reflections generatedby the shaped or patterned pulse are not received by sensor unit 104(FIG. 1). Range R_(WAVE) is the range from which the reflectionsgenerated by the shaped or patterned pulse begin to be received andintensified. The curve along R_(WAVE) results from the shape or patternof the decay of laser pulse 192 (FIG. 12). The gradient along R_(CON)results from the increasing amount of the maximum intensity portion oflaser pulse 192, corresponding to T_(CON) (FIG. 12), detected on sensorunit 104 (FIG. 1). The gradient along R_(CON) also results from thedifferent passing times between a laser pulse and elements in its path,as described with reference to FIGS. 5-7. Range R₀ to R₁ is the rangefrom which the intensity of laser pulse 192 is steady. Range R₁ toR_(MAX) is the range from which the intensity of laser pulse 192decreases at a constant rate. Beyond R_(MAX) is the range from whichreflections are no longer detected on sensor unit 104. It is thereforepossible to further reduce the sensitivity of system 100 (FIG. 1) atclose ranges, and prevent reflections from atmospheric substances in thearea substantially near system 100, by generating shaped or patternedlaser pulses, in conjunction with a pulse width based timing forswitching sensor unit 104 to the “on” state (as discussed with referenceto FIGS. 7-9). It is appreciated that system sensitivity as a functionof range is further improved with the implementation of a shaped orpatterned laser pulse (or analogously varying the energy of the pulse),in addition to the results achieved by the gating technique per se.

Reference is now made to FIGS. 15-18. These graphs depict techniques fortiming adjustments during the process of obtaining an individual videoframe of received reflections from a target. These techniques illustratethe ability to change the duration of time sensor unit 104 (FIG. 1) isactivated and/or the width of laser pulse 106 (FIG. 1) in order toachieve maximum sensitivity of system 100 (FIG. 1) at the optimum rangeR₀. It is appreciated that limiting the number of transmitted laserpulses without compromising image quality, reduces the sensitivity ofthe system to extraneous ambient light sources.

It is assumed that a video frame based system is utilized. The array ofphotodetectors of sensor unit 104 may be a standard video sensor, suchas a CCD (Charge Coupled Device) or a CMOS (Complementary Metal OxideSemiconductor) type of sensor. The CCD type sensor may include anexternal shutter. Such sensors typically operate at a constant frequencyof approximately 50-60 Hz. This means that each second the array ofphotodetectors captures 25-30 frames. To demonstrate the technique, itis assumed that the array of photodetectors operates at 50 Hz. Theduration of an individual frame is then 20 ms. Assuming the range ofinterest for system 100 is 300 m, the width of laser pulse 106 inaddition to the duration of time that sensor unit 104 is set to the “on”state must add up to 3 μs. It is noted that the effect of T_(OFF) is notconsidered for the purposes of this simplified example. This frequencyof operation requires a cycle time of 3 μs with no time gaps (i.e.waiting times) between the end of laser pulse 106 and the opening ofsensor unit 104. It is then possible to transmit up to 6666 pulses andto collect up to 6666 reflected pulses, in the course of an individualfield, i.e. a video frame.

FIG. 15 is a graph, generally designated 220, depicting the sequence ofpulse cycles (L) and collection of reflected photons (P) over anindividual field. The vertical axis represents the status of a device,where ‘1’ represents a status of the device being on, and ‘0’ representsa status of the device being off. The horizontal axis represents time. Acycle is defined as the time period required for one laser pulse to betransmitted and one reflected photon, or bundle of reflected photons, tobe received. A cycle is therefore defined as T_(L)+T_(P). T_(L) definesan amount of time a laser device is on. T_(p) defines an amount of timea sensor device is on. It is assumed that the lower the number of cyclesrequired for obtaining a quality image, the greater the ability of asystem to reduce the effects of ambient light sources, since a highernumber of cycles increases a system's potential exposure to ambientlight sources.

FIG. 16 is a graph, generally designated 230, depicting a timingtechnique where a laser pulse width is changed dynamically over thecourse of obtaining an individual frame. The vertical axis representsthe status of a device, where ‘1’ represents a status of the devicebeing on, and ‘0’ represents a status of the device being off. Thehorizontal axis represents time. The total width of each cycle remainsconstant, although the width of laser pulse 106 (T_(L)) becomes narroweras time progresses, with the gap between T_(L) and T_(P) growingaccordingly. By the final cycle, the width of laser pulse 106 is veryshort in comparison to its width in the first cycle, while the waitingtime for the array of photodetectors to open (T_(OFF)) is very long incomparison to T_(OFF) in the first cycle. The rate at which the waitingtime, before sensor unit 104 is activated, is increased, is equal to therate at which the width of laser pulse 106 is narrowed. Thus, the rangeR_(MIN), from which no reflections are received from system 100, may beincreased. In this manner, system 100 receives more reflections from theremote range than from the near range, and a desired sensitivity as afunction of range is achieved.

FIG. 17 is a graph, generally designated 240, depicting a timingtechnique where the duration that a sensor unit is activated is changeddynamically over the course of obtaining an individual frame. Thevertical axis represents the status of a device, where ‘1’ represents astatus of the device being on, and ‘0’ represents a status of the devicebeing off. The horizontal axis represents time. Similar to the techniqueshown in graph 230 of FIG. 16, the total width of each cycle remainsconstant although the duration that sensor unit 104 is set to the “on”state (T_(P)) becomes narrower as time progresses, with the gap betweenT_(L) and T_(P) growing accordingly. By the final cycle, the duration ofT_(P) is very short in comparison to its duration in the first cycle,while the waiting time for the array of photodetectors to open (T_(OFF))is very long in comparison to T_(OFF) in the first cycle. The rate atwhich the waiting time, before sensor unit 104 is activated, isincreased, is equal to the rate at which the duration that sensor unit104 is set “on” is narrowed. Thus, the range R_(MIN), from which noreflections are received from system 100, may be increased. In thismanner, system 100 receives more reflections from the remote range thanfrom the near range, and a desired sensitivity as a function of range isachieved.

FIG. 18 is a graph, generally designated 250, depicting a timingtechnique where both a laser pulse width and the duration that a sensorunit is activated is changed dynamically over the course of obtaining anindividual frame. The vertical axis represents the status of a device,where ‘1’ represents a status of the device being on, and ‘0’ representsa status of the device being off. The horizontal axis represents time.

It is noted that in graph 230 of FIG. 16, since time T_(P) remainsconstant, system 100 will remain sensitive to the effects of ambientlight sources for a longer period than the system of graph 240 of FIG.17. Since T_(P) remains constant, reflected energy not emitted by lasersource 102 (FIG. 1) may be received by sensor unit 104. It is furthernoted that in graph 240 of FIG. 17, since time TL remains constant,system 100 will also remain sensitive to the effects of ambient lightsources. Since time T_(L) remains constant, part of the reflected energymay not return to sensor unit 104 in an activated mode, thereby usingenergy for a longer time period than the system of graph 230 in FIG. 16.

Similar to the techniques shown in graph 230 and graph 240 (FIGS. 16 and17), the total width of each cycle remains constant. Both the width oflaser pulse 106 (T_(L)) and the duration that sensor unit 104 is set tothe “on” state (T_(P)) become narrower as time progresses, with the gapbetween T_(L) and T_(P) growing accordingly. By the final cycle, theduration of T_(L) and the duration of T_(P) are each very short incomparison to the first cycle, while the waiting time for the array ofphotodetectors to open, T_(OFF), is very long in comparison to the firstcycle. The rate at which the waiting time before sensor unit 104 isactivated is increased is equal to the sum of the rates at which T_(L)and T_(P) are each narrowed. For example, if T_(L) and T_(P) arenarrowed at the same rate, then T_(OFF) is increased at twice this rate.In this technique, the time in which sensor unit 104 is activated andthereby susceptible to the effect of ambient light sources is shortened,thus exploiting the energy spent and received, by system 100, to amaximum. In this manner, system 100 receives more reflections from theremote range than from the near range, and a desired sensitivity as afunction of range is achieved. This is provided at the “expense” ofnarrowing the depth of field, which means having R_(MIN) approach R₀.Having R_(MIN) approach R₀ is desirable when a target range is knownmore accurately. Narrowing the depth of field can also be compensated byenhancing the pulse intensity.

Timing adjustments during the process of obtaining an individual videoframe may be employed in order to achieve a desired sensitivity as afunction of range. This may involve dynamically changing the width of alaser pulse, the duration of time a sensor unit is set to the “on”state, or both. It is appreciated that the aforementioned techniques oftiming adjustments may be integrated and combined with theaforementioned technique of changing the shape, pattern or energy of alaser pulse, as discussed with reference to FIGS. 12-14.

Reference is now made to FIGS. 19-21. These graphs depict techniques foradjusting the number of cycles, or exposures, during the process ofobtaining an individual video frame. These techniques serve to eliminateblooming, or self-blinding, arising from high intensity ambient lightsources. Additionally, or alternatively, implementation of differentimage processing techniques may be utilized for this purpose. Inparticular, the rate of laser pulse transmissions (L) and collection ofreflected photons (P) may be changed dynamically, thereby reducing thenumber of exposures.

It is recalled that in the example discussed earlier with reference toFIGS. 15-18, it is possible to transmit up to 6666 pulses and to collectup to 6666 reflected photons, in the course of an individual field. Thismeans that a maximum number of 6666 cycles or exposures can be performedover a single field. However, it is also possible to perform fewerexposures. FIG. 19 is a graph, generally designated 260, depictingtiming adjustments during the process of obtaining an individual videofield, where a total of 6666 exposures are performed. The vertical axisrepresents the status of a device, where ‘1’ represents a status of thedevice being on, and ‘0’ represents a status of the device being off.The horizontal axis represents time. FIG. 20 is a graph, generallydesignated 260, depicting timing adjustments during the process ofobtaining an individual video field, where a total of 100 exposures areperformed. The vertical axis represents the status of a device, where‘1’ represents a status of the device being on, and ‘0’ represents astatus of the device being off. The horizontal axis represents time.

Reducing the number of exposures in a field might cause less photons tobe collected at sensor unit 104 (FIG. 1), and thereby cause darkening inthe generated image so that low reflection areas may not be visible.Therefore, the number of exposures in a field should be dynamicallycontrolled. The number of exposures in a field may be controlled inaccordance with several factors. For example, one factor may be thelevel of ambient light (information which may be received as an input tosystem 100 from an additional sensor which detects ambient light).Another factor may be the level of current consumed by sensor unit 104(information which may be obtained via a power supply).

FIG. 21 is a pair of graphs, generally designated 280 and 290, depictingtiming adjustments during the process of obtaining an individual videofield, where the number of exposures in a field is controlled by atechnique based on image processing. The vertical axis represents thestatus of a device, where ‘1’ represents a status of the device beingon, and ‘0’ represents a status of the device being off. The horizontalaxis represents time. This technique involves sensor unit 104 acquiringtwo frames. In one frame a large number of exposures are obtained, andin the other frame, a small number of exposures are obtained. In thisembodiment of the disclosed technique, sensor unit 104 includes at leastone photodetector, or an array of photodetectors, that operates fasterthan standard CCD or CMOS sensors. It is assumed that sensor unit 104operates at a frequency of 100 Hz. The corresponding duration of eachframe is then 10 ms. Graphs 280 and 290 depict sensor unit 104 acquiringtwo frames. In the first frame, graph 280, system 100 (FIG. 1) performs1000 exposures, and in the second frame, graph 290, system 100 performs50 exposures. As mentioned earlier, the number of exposures in a fieldmay be controlled in accordance with several factors, such as the levelof ambient light, the saturation state of the photodetectors, imageprocessing constraints, and the like. After sensor unit 104 acquires twoframes with a particular number of exposures in each, the two frames maybe combined into a single frame. Dark areas may be combined from theframe having the larger number of exposures, and saturated areas may becombined from the frame having the smaller number of exposures.

FIG. 22 is a schematic illustration of the two image frames acquired inFIG. 21, and the combination of the two frames. It is assumed that thesize of an image frame is 4 pixels, for simplicity. In the first frame292, which originates from a large number of exposures, the upper pixelsbecome saturated, while the lower pixels retain a reasonable level ofgray. In the second frame 294, which originates from a smaller number ofexposures, the upper left pixel does not become saturated, whereas thelower pixels are dark areas. In the combined image, the pixels fromfirst frame 292 are combined with the pixels from second frame 294. Thecombined image frame 296 has less saturated pixels (only the upper rightpixel), and less dark area pixels (only the lower right pixel). Theoverall image quality is thereby increased. The combination of thesaturated upper left pixel in first frame 292 and the non-saturatedupper left pixel in second frame 294 generates a non-saturated upperleft pixel in combined frame 296.

The technique depicted in FIGS. 21 and 22 of two frame exposuresfollowed by a frame combination enlarges the dynamic range of system 100and provides a high quality image even in a saturated environment. It isappreciated that such image processing may be implemented via othertechniques. For example, by using an even faster sensor, it is possibleto combine a larger number of frames.

It is recalled that the blinding effect includes blinding caused by theoperation of a similar system in the vicinity of system 100, hereinknown as mutual blinding. System 100 may overcome mutual blinding byapplying statistical techniques or synchronization techniques.Statistical techniques may include reducing the number of exposures inthe course of acquiring an individual video field and possiblycompensating by using a greater laser intensity or a higherintensification level from sensor unit 104 (FIG. 1). The techniques mayalso include a random or predefined change in the timing of cyclesthroughout a single frame, changing the exposure frequency, or anycombination of these techniques. Synchronization techniques may includeestablishing a communication channel between the two systems, forexample, in the RF range. Such a channel would enable the two systems tocommunicate with each other. Another possible synchronization techniquefor overcoming mutual blinding is automatic synchronization.

Reference is now made to FIG. 23, which is a pair of graphs, generallydesignated 310 and 320, depicting a synchronization technique forovercoming mutual blinding. The vertical axis represents the status of adevice, where ‘1’ represents a status of the device being on, and ‘0’represents a status of the device being off. The horizontal axisrepresents time. In the synchronization technique depicted in FIG. 23,one system enters a “listening period” every so often. When the systemis in the listening period, the system refrains from transmitting laserpulses and collecting reflections. In the event that a second systemdoes not transmit any pulses while the first system is in its listeningperiod, section 312 of graphs 300 and 310, the first system may resumeactivity at the end of its listening period. In the event that thesecond system transmits pulses while the first system is in itslistening period, section 314 of graphs 300 and 310, the first systemwaits until the end of the cyclic sequence of the second system beforeresuming activity. In graph 300, system #1 performs a cyclic sequence of50 exposures before entering a listening period. In graph 310, system #2performs a cyclic sequence only when system #1 is in a listening period.In this manner, synchronization between system #1 and system #2 ensuresthat no pulses transmitted by one system are received by the othersystem, resulting in interference and mutual blinding. It is noted thatin the synchronization technique, 50% of the possible exposure time in aframe is allotted to each system.

The synchronization technique depicted in FIG. 23 may be applied, forexample, in a night vision imaging system mounted on a moving platform(such as a vehicle), according to one embodiment of the disclosedtechnique. For the sake of illustrative purposes, reference will be madeto a vehicle, as an example which is applicable to any moving platform.In this embodiment of the disclosed technique, a night vision imagingsystem mounted on a vehicle may include an interface with the vehicle'scomputer system (automotive BUS). Two pulse detectors are mounted in thevehicle in which system 100 (FIG. 1) is installed. One pulse detector isinstalled in the front section of the vehicle, and the other pulsedetector is installed in the rear section of the vehicle. The pulsedetectors detect if other systems similar to system 100 are operating invehicles approaching the vehicle of system 100 from the front or fromthe rear. Since a vehicle approaching from the rear is not likely tocause interference with system 100, synchronization may not beimplemented in such a case.

An alternative synchronization technique for overcoming mutual blindinginvolves “sharing”. For example, part of the listening period of a framemay be dedicated to detecting pulses transmitted by other systems. If nopulse is detected from another system, system 100 may randomly decidewhen laser device 102 (FIG. 1) may begin transmitting laser pulseswithin the same frame span. If a pulse from another system is detectedhowever, system 100 initiates transmission of laser pulses at a randomtime only after the approaching pulse has ended. Alternatively, eachsystem may randomly change their pulse start transmission timing in eachframe. It is appreciated that these synchronization techniques forovercoming mutual blinding allow a system to synchronize with othersystems that operate at different rates. Another possiblesynchronization technique for overcoming mutual blinding involves asynchronizing pulse transmitted by one system at a given time, while theother system adapts itself in accordance with the received synchronizingpulse.

Reference is now made to FIG. 24, which is a block diagram of a methodfor target detection and identification, accompanied by an illustrationof a conceptual operation scenario, generally designated 350, operativein accordance with another embodiment of the disclosed technique. Inconceptual operation scenario 350, an attack helicopter 352 equippedwith an observation system in accordance with an embodiment of thedisclose technique, such as system 100, is involved in an anti-tankoperation at night.

In the first stage 360, the helicopter crew detects a hot spot 354 at a15 km range using a FLIR (Forward Looking Infrared) device. In thesecond stage 370, when the helicopter is distanced only 14-15 km fromhot spot 354, the surveillance and observation system is activated. Onlyduring the course of this stage are laser energy beams emitted indirection 356 and reflected from the target in direction 358. The gatedsystem is operated for only a few seconds. This is sufficient forstoring in the system enough images from which an image 366 of target362 is generated and stored. The radiating laser beam may exposehelicopter 352. Limiting this exposure to a few seconds helps to protecthelicopter 352 from counter-detection. In the third stage 380, thehelicopter crew reverts to a passive operation mode, i.e. a relativelysafer operation mode, while advancing towards the identified target 362.When the helicopter arrives at a distance of 12-14 km from target 362,the identification stage of image 366 is completed by reviewing itsrecorded details, such as by comparison 364 with other images ofpotential targets 368 stored in a data bank (not shown). In the exampleshown in FIG. 24, the hot spot is identified as a legitimate target,namely, an enemy tank. In the final stage 390, the helicopter crewactivates a weapons system, for example a missile homing on the thermalradiation emitted by hot spot 354. The activated weapon destroys thetarget from a relatively distant range, for example from a range of 8-9km.

It is noted that in the course of the operation, described by sequence360 to 390, the system in helicopter 352 had no need to measure theexact range to target 362. Such a measurement would have necessitatedoperating the laser for an extended period of time, thereby increasingthe likelihood of exposure and detection of helicopter 352 by an enemy.

Reference is now made to FIG. 25, which is a schematic illustration of asystem, generally referenced 400, constructed and operative inaccordance with another embodiment of the disclosed technique. System400 is stabilized by a gimbals, and the optical axis of an illuminatinglaser beam is coupled with the optical axis of an observing section.

System 400 includes an external section 402 and an observation section404. External section 402 includes a laser device 406 and an electroniccontroller 408. Observation section 404 includes at least onephotodetector, or an array of photodetectors, 410, an optical couplingmeans 412, a coupling lens assembly 414, and an optical assembly 416.Laser device 406 is optically coupled with optical coupling means 412.Electronic controller 408 is coupled with array of photodetectors 410.Array of photodetectors 410 is further coupled with optical couplingmeans 412. Coupling lens assembly 414 is coupled with optical couplingmeans 412 and with optical assembly 416. Optical coupling means 412includes a collimating lens 426, a first mirror 428 and an integratinglens assembly 430. Integrating lens assembly 430 includes a secondmirror 432. First mirror 428 is optically coupled with collimating lens426 and with integrating lens assembly 430. Optical assembly 416includes an array of objective lenses 442. Gimbals 420 stabilizesobservation section 404. Stabilization is required when system 400 ispositioned on a continuously moving or vibrating platform, whetherairborne, terrestrial or nautical, such as an airplane, helicopter, seacraft, land vehicle, and the like. Observation section 404 may also bestabilized by using feedback from a gyroscope to gimbals 420, bystabilization using image processing techniques, based on the spatialcorrelation between consecutively generated images, by stabilizationbased on sensed vibration, or in any combination of the above. Externalsection 402 does not require specialized stabilization and may thereforebe packaged separately and located separately from observation section404. The stabilization may be based on detection of vibrations of thesensor means that influence the image as it is captured. Such sensormeans in FIG. 25 may include observation section 404, photodetector(s)410, optical coupling means 412, coupling lens assembly 414, and opticalassembly 416, and their rigid packaging.

Laser device 406 transmits a pulsed laser beam 422 toward a target.Laser device 406 may be a Diode Laser Array (DLA). The transmitted laserbeam 422 propagates through optical fiber 424. Optical fibers are usedin system 400 to transmit laser beam 422 because they enable the laserbeam spot size to be reduced to the required field-of-view (FOV).Optical fibers also allow for easy packaging. Furthermore, opticalfibers transmit laser light such that no speckle pattern is producedwhen the laser light falls on a surface (laser devices, in general,produce speckle patterns when laser light falls on a surface). Laserdevice 406 is separate from observation section 404. Since laser device406 may be inherently heavy this facilitates packaging and results indecreased weight in observation section 404.

Transmitted laser beam 42 propagates through optical fiber 424 towardcollimating lens 426. Collimating lens 426 collimates transmitted laserbeam 422. The collimated laser beam is conveyed toward first mirror 428.First mirror 428 diverts the direction of the collimated laser beam andconverges the beam onto integrated lens assembly 430. Converged beam 434reaches second mirror 432. Second mirror 432 is typically very small.Second mirror 432 couples the optical axis 436 of converged beam 434with the optical axis 438 of observation section 404. Optical axis 438is common to array of photodetectors 410 and to optical assembly 416.Second mirror conveys converged beam 434 toward coupling lens assembly414. Coupling lens assembly conveys the beam toward array of objectivelenses 442.

Array of objective lenses 442 collimates the beam once more andtransmits the collimated laser beam 440 toward a target (not shown).Beam 440 illuminates the target, and the reflections of light impingingon the surface of the target return to optical assembly 416. Opticalassembly 416 routes the reflected beam 450 toward array ofphotodetectors 410 via coupling lens assembly 414.

Array of photodetectors 410 processes reflected beam 450 and convertsreflected beam 450 into an image displayable on a television. Array ofphotodetectors 410 may be a CCD (Charge Coupled Device) type sensor. Inthis case, the CCD sensor is coupled by relay lenses to a gated imageintensifier, as is known in the art. The CCD type sensor may includeexternal shutters. Alternatively, array of photodetectors 410 may be aGated Intensified Charge Injection Device (GICID), a Gated IntensifiedCCD (GICCD), a Gated Image Intensifier, a Gated Intensified Active PixelSensor (GIAPS), and the like. It is noted that such sensor types enableadvanced processing of the displayable television image, such asenlarging the image, identifying features, and the like. Advanceprocessing may include, for example, comparing the image with a set ofimages in a databank of known identified target (see step 380 withreference to FIG. 24). The generated displayable television image may besubjected to additional processing. Such processing may includeaccumulating image frames via a frame grabber (not shown), integrationto increase the quantity of light and to improve contrast, electronicstabilization provided by image processing techniques based on thespatial correlation between consecutively generated images, and thelike.

Controller 408 controls the timing of array of photodetectors 410, andreceives the displayable television image via suitable wiring 444.Controller 408 may include an electronics card. Controller 408 controlsthe timing of array of photodetectors 410 in synchronization with thelaser pulses provided by laser device 406. The timing is such that arrayof photodetectors 410 will be closed during the time period that thelaser beam traverses a distance adjacent to system 410 en route to thetarget (distance R_(MIN), with reference to FIG. 1). Switching thesensor unit to the “off” state immediately after transmitting the laserbeam ensures that unwanted reflections, from atmospheric substances andparticles and backscatter, are not captured by array of photodetectors410, and that the self-blinding phenomenon is avoided.

Reference is now made to FIG. 26, which is a schematic illustration of asystem, generally referenced 500, constructed and operative inaccordance with another embodiment of the disclosed technique. Theoptical axis of an illuminating laser beam in system 500 is essentiallyparallel with the optical axis of its array of photodetectors.

System 500 includes an electronics box 502, an observation module 504, apower supply 506, a narrow field collimator 508, a display 510, a videorecorder 512, and a support unit 514. Electronics box 502 includes alaser device 516, a laser cooler 518, a controller 520, a service panelfor technicians 522, an image processing unit 524 and a PC (PersonalComputer) card 526. Observation module 504 includes an optical assembly528, a filter 530, an optical multiplier 532, an array ofphotodetectors, or at least one photodetector, 534, and an electronicscard 536. A spatial modulator shutter (not shown) may be located infront of array of photodetectors 534. A narrow field collimator 508 isinstalled on observation module 504. A power supply 506 is coupled withelectronics box 502 via a connector 538. Electronics box 502 is coupledwith observation module 504 via a cable 540. Electronics box 502 isoptically coupled with narrow field collimator 508 via an optical fiber542. Video recorder 512 is coupled with electronics box 502 and withdisplay 510.

Laser device 516 transmits a pulsed laser beam 544 toward a target (notshown). Laser device 516 may be a DLA. Laser cooler 518 provides coolingfor laser device 516. The transmitted laser beam 544 propagates throughoptical fiber 542 toward narrow field collimator 508. Collimator 508collimates laser beam 544 so that the optical axis 546 of laser beam 544is essentially parallel with the optical axis 548 of array ofphotodetectors 534, and conveys collimated laser beam 544 toward thetarget.

The reflected beam 550 from the target reaches optical assembly 528.Optical assembly 528 includes an array of narrow field objective lenses(not shown) packaged above support unit 514. Optical assembly 528conveys reflected beam 550 to filter 530. Filter 530 performs spectraland spatial filtering on reflected beam 550. Filter 530 may locallydarken an entrance of array of photodetectors 534 to overcome glareoccurring in system 500. Image processing unit 524 provides control andfeedback to filter 530. Filter 530 may be an adaptive Spatial LightModulator (SLM), a spectral frequency filter, a polarization filter, alight polarizer, a narrow band pass filter, or any other mode selectivefilter. An SLM filter may be made up of a transmissive Liquid CrystalDisplay (LCD), a Micro-Electro-Mechanical System (MEMS), or othersimilar devices. Filter 530 may also be a plurality of filters. Thecharacteristics of filter 530 suit the energy characteristics ofreflected beam 550. Using feedback from image processing unit 524,filter 530 may be programmed to eliminate background radiationsurrounding the target which is not within the spectral range of laserdevice 516. Residual saturation remaining on the eventual image as aresult of ambient light sources in the field of view, for exampleartificial illumination, vehicle headlights, and the like, may bereduced by a factor of approximately 1/1000^(th) through adaptive SLMfiltering. It is noted that other light sources in the field of viewundergo additional filtering by the LPGI technique and by opticenlargement performed before reflected beam 550 is converted to adisplayable image. This additional filtering is meant to facilitateseparation between background light and the illuminated target, and toprevent blinding due to the presence of intense light sources in theimmediate vicinity of system 500.

Filter 530 conveys reflected beam 550 to optical multiplier 532. Opticalmultiplier 532 enlarges reflected beam 550. It is noted that filter 530,or optical multiplier 532, or both, may be installed directly on theoutput end of optical assembly 528. Optical multiplier may also beinstalled directly on the input end of array of photodetectors 534.Array of photodetectors 534 receives reflected beam 550, and processesand converts reflected beam 550 to image data. Array of photodetectors534 may be a CCD sensor. The CCD sensor may include external shutters.Array of photodetectors 534 transfers the image data to electronics card536 via cable 552. Electronics card 536 transfers the image data toelectronics box 502 via cable 540. Cable 540 may be any type of wired orwireless communication link. Controller 520 synchronizes the timing ofarray of photodetectors 534. Controller 520 ensures that array ofphotodetectors 534 is closed (i.e. the sensor unit is deactivated) whentransmitted laser beam 544 traverses a range in the immediate vicinityof a target (i.e. range R_(MIN), referring to FIG. 1) for both theforward and return paths. PC card 526 enables a user to interface withelectronics box 502. PC card 526 is embedded with image processingcapabilities. PC card 526 allows the image received from array ofphotodetectors 534 to be analyzed and processed. For example, suchprocessing may include comparing the image to pictures of identifiedtargets stored in a data bank, local processing of specific regions ofthe image, operation of the SLM function, and the like. The generatedimage may be presented on display 510 or recorded by video recorder 512.The image may be transferred to a remote location by an externalcommunication link (not shown) such as a wireless transmission channel.

Power supply 506 supplies power to the components of electronics box 502via connector 538. Power supply 506 may be a battery, a generator, orany other suitable power source. For example, an input voltage frompower supply 506 allows laser device 516 to operate. Support unit 514supports observation module 504, as well as narrow field collimator 508installed above observation module 504. Support unit 514 provides forheight and rotational adjustments. Support unit 514 may include a tripod(not shown), support legs 554 for fine adjustments, and an integralstabilization system (not shown) including, for example, viscous shockabsorbers.

It is noted that DLA laser device 516 allows optical fibers to be usedto convey transmitted laser beam 544. This facilitates packaging oflaser device 516, which is typically heavy. Laser device 516 is alsolocated separately from observation module 504, resulting in less weighton observation module 504. It is further noted that DLA laser device 516generates a beam of laser energy having substantially high power forextended periods. Since the generated beam has a high frequency and arelatively low intensity, it may be routed via optical fibers which havelimited durability for high intensity power, particularly at the peak.

It is further noted that a DLA laser device generates radiation in thenear infrared spectral region, which is invisible to the human eye.However, this wavelength is also very close to the visible spectrum.Image intensifiers are very sensitive to this wavelength and providegood image contrast. Thus an image intensifier used in conjunction witha DLA laser device can provide high image quality even for targets atlong ranges.

It is further noted that a DLA laser device generates non-coherentradiation. Therefore, the generated beam has very uniform radiation andresults in an image of higher quality than if a coherent laser beam isused. It is further noted that a DLA laser device can operate in a“snapshot” observation mode. Snapshot observation involves transmittinga series of quick flash bursts, which diminishes the duration of timethat the laser device is active. This reduces the exposure of a systemand the risk of being detected by a foreign element.

It is further noted that in an embodiment of the disclosed techniquewhere the system is stabilized on a gimbals, such as system 400 (FIG.25), a DLA laser device enables switching of the array ofphotodetectors, allowing the array of photodetectors to operate on veryshort time spans with respect to the long damped vibrations of thegimbals. Such vibrations may cause blurring in the generated image. Itis further noted that a DLA laser device is highly efficient inconverting power to light. A DLA laser device delivers more light andless heat than other types of laser devices. Accordingly, the laser inthe disclosed technique is transmitted through relatively wide opticsand at relatively low intensities, so that the safety range is only afew meters from the laser. In contrast, in systems with laser rangefinders or laser designators, the safety range may reach tens ofkilometers.

It is further noted that a DLA laser device is suitable for applicationswhere laser transmission through a water medium is required, for examplewhen performing sea surveillance from an airborne system, whenperforming underwater observation, or other nautical applications. Forsuch applications, a laser beam in the blue-green range of the visiblespectrum provides optimal performance.

It is noted that pulse emitting means (or transmitters) and the sensordescribed herein above are located in the same place, which is easierfor the simultaneous control of the pulse and the sensor gating, andtheir timing or their synchronization. This location of the pulseemitting means and the sensor typifies cases when the path between thesensor and the object observed are obscured. However, the disclosedtechnique is not limited to such a configuration. The pulse emitter andthe sensor may well be situated in two different locations, as long astheir control, timing or synchronization are appropriately maintainedfor creating a sensitivity as a function of the range such that anamount of received energy of pulse reflections, reflected from objectslocated beyond a minimal range, progressively increases with the rangealong said depth of a field to be imaged. The relevant ranges (includingminimal, optimal and maximal ranges, and the depth of a field) will thenbe described with respect to the sensor, rather than the emitter. Thismay be achieved by various technologies, including communication betweenthe emitter and the sensor, with a controller, using an emitter signalbearing timing or other information picked up by the sensor, atomicclocks, a common clock, and the like. The pulse would then merely“reflect” at some angle rather than “reflect back” at 180 degrees fromthe observed objects toward the sensor. Thus any use of terms such as“back” in this context herein should be read as also referring toreflections at any angle from the objects to the sensor. Calculationsillustrating the “to and fro” path towards the target and back to thesensor merely demonstrate one situation, and can be easily andanalogously altered to calculations for other paths.

It will be appreciated by persons skilled in the art that the disclosedtechnique is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the disclosed technique isdefined only by the claims, which follow.

1. A portable, moveable or stationary mounted imaging system comprising:a transmission source, said transmission source providing at least oneenergy pulse; a sensor for receiving pulse reflections of said at leastone energy pulse reflected from objects within a depth of a field to beimaged, characterized in that said depth of field having a minimalrange, R_(MIN), said sensor enabled to gate detection of said pulsereflections, with a gate timing controlled such that said sensor startsto receive said pulse reflections after a delay timing substantiallygiven by the time it takes said at least one energy pulse to reach saidminimal range and complete reflecting to said sensor from said minimalrange, wherein each of said at least one energy pulse and said gatetiming are controlled for creating a sensitivity as a function of rangefor said system, such that an amount of received energy of said pulsereflections, reflected from objects located beyond said minimal range,progressively increases with the range along said depth of a field to beimaged.
 2. The system according to claim 1, wherein said at least oneenergy pulse and said gate timing are controlled for creating asensitivity as a function of range for said system, such that an amountof received energy of said pulse reflections, reflected from objectslocated beyond said minimal range, progressively increases with therange along said depth of a field to be imaged until an optimal range,R₀.
 3. The system according to claim 2, wherein said at least one energypulse and said gate timing are controlled for creating a sensitivity asa function of range for said system, such that an amount of receivedenergy of said pulse reflections, reflected from objects located beyondsaid optimal range, is maintained detectable until a maximal range,R_(MAX).
 4. The system according to claim 3, wherein said at least oneenergy pulse and said gate timing are controlled for creating asensitivity as a function of range for said system, such that saidamount of received energy of said pulse reflections, reflected fromobjects located beyond said optimal range, is maintained substantiallyconstant until said maximal range.
 5. The system according to claim 3,wherein said at least one energy pulse and said gate timing arecontrolled for creating a sensitivity as a function of range for saidsystem, such that said amount of received energy of said pulsereflections, reflected from objects located beyond said optimal range,gradually decreases until said maximal range.
 6. The system according toclaim 1, wherein said at least one energy pulse and said gate timing arecontrolled for creating a sensitivity as a function of range for saidsystem, such that an amount of received energy of said pulse reflectionsis directly proportional to the ranges of said objects to be imaged. 7.The system according to claim 1, wherein said at least one energy pulsedefines a substantial pulse width, T_(LASER), commencing at a starttime, T₀; said delay timing is substantially given by the time elapsingfrom said start time, T₀, until twice said minimal range, R_(MIN),divided by the speed at which said at least one energy pulse travels, v,in addition to said pulse width, T_(LASER):$\frac{2 \times R_{MIN}}{v} + {T_{LASER}.}$
 8. The system according toclaim 1, wherein said at least one energy pulse and said gate timing arecontrolled for creating a sensitivity as a function of range for saidsystem through synchronization between the timing of said at least oneenergy pulse and the timing of said gate detection.
 9. The systemaccording to claim 1, wherein said at least one energy pulse defines asubstantial pulse width, T_(LASER), a pulse pattern, a pulse shape, anda pulse energy; said sensor is enabled to gate detection of said pulsereflections, with a gating time span said sensor is activated, T_(ON), aduration of time said sensor is deactivated, T_(OFF), and asynchronization timing of the gating with respect to said at least oneenergy pulse; and wherein at least one of said delay timing, said pulsewidth, said pulse shape, said pulse pattern, said pulse energy, saidgating time span, said sensor is activated, T_(ON), said duration oftime said sensor is deactivated, T_(OFF), and said synchronizationtiming, is determined according to at least one of said depth of a fieldto be imaged, specific environmental conditions said system is used in,a speed said system is moving at, and specific characteristics ofdifferent objects expected to be found in said depth of field.
 10. Thesystem according to claim 9, wherein said pulse width, said duration oftime said sensor is deactivated, and said gating time span said sensoris activated define a cycle time, wherein said at least one energy pulseis provided for a duration of said pulse width, the opening of saidsensor is delayed for a duration of said duration of time said sensor isdeactivated, and said pulse reflections are received for a duration ofsaid gating time span said sensor is activated.
 11. The system accordingto claim 9, wherein said determination according to at least one of saiddepth of a field, said specific environmental conditions, said speedsaid system is moving at, and said specific characteristics of differentobjects expected to be found in said depth of field, is a dynamicdetermination.
 12. The system according to claim 11, wherein said pulsewidth and said gating time span are limited to reduce the sensitivity ofsaid system to ambient light sources.
 13. The system according to claim12, wherein said pulse width is shortened progressively, said delaytiming is lengthened progressively, and said cycle time does not change.14. The system according to claim 12, wherein said gating time span isshortened progressively, said delay timing is lengthened progressively,and said cycle time does not change.
 15. The system according to claim12, wherein said pulse width and said gating time span are shortenedprogressively, said delay timing is lengthened progressively, and saidcycle time does not change.
 16. The system according to claim 1, whereinthe gating of said sensor is utilized to create a sensitivity as afunction of range for said system by changing a parameter selected fromthe group consisting of changing the shape of said at least one energypulse, changing the pattern of said at least one energy pulse, changingthe energy of said at least one energy pulse, changing a gating timespan said sensor is activated, T_(ON), changing a duration of time saidsensor is deactivated, T_(OFF), changing a pulse width, T_(LASER), ofsaid at least one energy pulse, changing said delay timing, and changinga synchronization timing between said gating and the timing of providingsaid at least one energy pulse.
 17. The system according to claim 16,wherein said changing of a parameter is utilized according to at leastone of: said depth of field, specific environmental conditions saidsystem is used in, a speed said system is moving at, and characteristicsof different objects expected to be found in said depth of field. 18.The system according to claim 8, further comprising a controller forcontrolling said synchronization.
 19. The system according to claim 18,wherein at least one repetition of said cycle time forms part of anindividual video frame, and a number of said repetitions forms anexposure number per said video frame.
 20. The system according to claim19, further comprising a control mechanism for dynamically controllingand varying said exposure number.
 21. The system according to claim 20,wherein said exposure number is varied by said control mechanismaccording to a level of ambient light.
 22. The system according to claim21, further comprising an image intensifier.
 23. The system according toclaim 22, wherein said exposure number is varied by said controlmechanism according to a level of current consumed by said imageintensifier.
 24. The system according to claim 20, wherein said controlmechanism comprises image processing means for locating areas in saidsensor in a state of saturation.
 25. The system according to claim 2,wherein a pulse width, T_(LASER), of said at least one energy pulse issubstantially defined in accordance with the following equation:${2 \times \frac{R_{0} - R_{MIN}}{v}},$ where v is the speed at whichsaid at least one energy pulse travels.
 26. The system according toclaim 2, wherein said sensor is enabled to gate detection of said pulsedreflections, with a gating time span said sensor is activated, T_(ON),and a duration of time said sensor is deactivated, T_(OFF), which aresubstantially defined in accordance with the following equations:$T_{ON} = {2 \times \frac{R_{0} - R_{MIN}}{v}}$ and${T_{OFF} = {\frac{2 \times R_{MIN}}{v} + T_{LASER}}},$ where T_(LASER)is the pulse width of said at least one energy pulse, and v is the speedat which said at least one energy pulse travels.
 27. The systemaccording to claim 1, further comprising a transmission device fortransmitting images constructed from said pulse reflections received insaid sensor.
 28. The system according to claim 1, further comprising apulse detector for detection of pulses emitting from a similar system.29. The system according to claim 1, further comprising a polarizer forfiltering out incoming energy, which does not conform to thepolarization of said pulse reflection.
 30. The system according to claim29, wherein said transmission source provides at least one polarizedenergy pulse.
 31. The system according to claim 10, wherein saidsensitivity of said system relates to a gain and responsiveness of saidsensor in proportion to an amount of energy received by said sensor,wherein said gain received by said sensor as a function of range R isdefined by the follow convolution formula:${I_{r}(R)} = \frac{\int_{T_{LASER} + T_{OFF}}^{T_{LASER} + T_{OFF} + T_{ON}}{{{L\left( {t - \frac{2R}{v}} \right)} \cdot {C(t)}}\quad{\mathbb{d}t}}}{T_{LASER}}$wherein L(t) defines a Boolean function representing an on/off status ofsaid transmission source, irrespective of a state of said sensor,wherein L(t)=1 if said transmission source is on and L(t)=0 if saidtransmission source is off, wherein C(t) defines a Boolean functionrepresenting an ability of said sensor to receive incoming pulsereflections according to a state of said sensor, wherein C(t)=1 if saidsensor is in an activated state and C(t)=0 if said sensor is in adeactivated state, and where v is the speed at which said at least oneenergy pulse travels.
 32. The system according to claim 31, wherein avalue for radiant intensity is obtained by multiplying said convolutionformula by a geometrical propagation attenuation function.
 33. Animaging system comprising: a transmission source, said transmissionsource providing at least one energy pulse; a sensor for receiving pulsereflections of said at least one energy pulse reflected from objectswithin a depth of a field to be imaged, characterized in that said depthof field having a minimal range, R_(MIN), said sensor enabled to gatedetection of said pulse reflections, with a gate timing controlled suchthat said sensor starts to receive said pulse reflections after a delaytiming substantially given by the time it takes said at least one energypulse to reach said minimal range and complete reflecting to said sensorfrom said minimal range, wherein said at least one energy pulse and saidgate timing are controlled for creating a sensitivity as a function ofrange for said system, such that an amount of received energy of saidpulse reflections, reflected from objects located beyond said minimalrange, progressively increases with the range along said depth of afield to be imaged, said at least one energy pulse defines a substantialpulse width, T_(LASER), a pulse pattern, a pulse shape, and a pulseenergy; said sensor is enabled to gate detection of said pulsereflections, with a gating time span said sensor is activated, T_(ON), aduration of time said sensor is deactivated, T_(OFF), and asynchronization timing of the gating with respect to said at least oneenergy pulse, wherein said sensitivity of said system relates to a gainand responsiveness of said sensor in proportion to an amount of energyreceived by said sensor, wherein said gain received by said sensor as afunction of range R is defined by the follow convolution formula:${I_{r}(R)} = \frac{\int_{T_{LASER} + T_{OFF}}^{T_{LASER} + T_{OFF} + T_{ON}}{{{L\left( {t - \frac{2R}{v}} \right)} \cdot {C(t)}}\quad{\mathbb{d}t}}}{T_{LASER}}$wherein L(t) defines a Boolean function representing an on/off status ofsaid transmission source, irrespective of a state of said sensor,wherein L(t)=1 if said transmission source is on and L(t)=0 if saidtransmission source is off, wherein C(t) defines a Boolean functionrepresenting an ability of said sensor to receive incoming pulsereflections according to a state of said sensor, wherein C(t)=1 if saidsensor is in an activated state and C(t)=0 if said sensor is in adeactivated state, and where v is the speed at which said at least oneenergy pulse travels.
 34. The imaging system according to claim 33,wherein a value for radiant intensity is obtained by multiplying saidconvolution formula by a geometrical propagation attenuation function.35. A portable, moveable or stationary imaging method, the methodcomprising the procedures of: emitting at least one energy pulse to atarget area; receiving at least one reflection of said at least oneenergy pulse reflected from objects within a depth of a field to beimaged, characterized in that said depth of field having a minimalrange, R_(MIN), said receiving comprises gating detection of said atleast one reflection such that said at least one energy pulse isdetected after a delay timing substantially given by the time it takessaid at least one energy pulse to reach said minimal range and completereflecting; and progressively increasing the received energy of said atleast one reflection reflected from objects located beyond said minimalrange along said depth of a field to be imaged, by controlling each ofsaid at least one energy pulse and the timing of said gating.
 36. Themethod according to claim 35, wherein said procedure of increasingcomprises increasing the received energy of said at least one reflectionreflected from objects located beyond said minimal range along saiddepth of a field to be imaged up to an optimal range, R₀.
 37. The methodaccording to claim 36, further comprising the procedure of maintainingdetectable the received energy of said at least one reflection reflectedfrom objects located beyond said optimal range along said depth of afield to be imaged up to a maximal range, R_(MAX).
 38. The methodaccording to claim 37, wherein said procedure of maintaining comprisesmaintaining substantially constant said received energy of said at leastone reflection reflected from objects located beyond said optimal rangealong said depth of a field to be imaged up to said maximal range. 39.The method according to claim 37, wherein said procedure of maintainingcomprises gradually decreasing said received energy of said at least onereflection reflected from objects located beyond said optimal rangealong said depth of a field to be imaged up to said maximal range. 40.The method according to claim 35, wherein said procedure of increasingcomprises increasing the received energy of said at least one reflectionin direct proportion to the ranges of said objects within said depth offield to be imaged.
 41. The method according to claim 35, wherein saidat least one energy pulse defines a substantial pulse width, T_(LASER),commencing at a start time, T₀; and said delay timing is substantiallygiven by the time elapsing from said start time, T₀, until twice saidminimal range divided by the speed at which said at least one energypulse travels, v, in addition to said pulse width, T_(LASER):$T_{LASER} + {\frac{2 \times R_{MIN}}{v}.}$
 42. The method according toclaim 35, wherein said at least one energy pulse defines a substantialpulse width, T_(LASER), a pulse pattern, a pulse shape, and a pulseenergy; said procedure of gating comprises a gating time span a sensorutilized for said receiving is activated, T_(ON), a duration of timesaid sensor is deactivated, T_(OFF), and a synchronization timing ofsaid gating with respect to said at least one energy pulse; and whereinat least one of said delay timing, said pulse width, said pulse shape,said pulse pattern, said pulse energy, said gating time span said sensoris activated, T_(ON), said duration of time said sensor is deactivated,T_(OFF), and said synchronization timing is determined according to atleast one of said depth of a field, specific environmental conditionssaid method is used in, a moving speed of said sensor, and specificcharacteristics of different objects expected to be found in said depthof field.
 43. The method according to claim 35, wherein said procedureof controlling comprises progressively changing at least one parameterselected from the group consisting of changing a pattern of said atleast one energy pulse, changing a shape of said at least one energypulse, changing the energy of said at least one energy pulse, changing agating time span a sensor utilized for said receiving is activated,T_(ON), changing a duration of time said sensor is deactivated, T_(OFF),changing an energy pulse width, T_(LASER), of said at least one energypulse, changing said delay timing, and changing a synchronization timingbetween said gating and said emitting.
 44. The method according to claim43, wherein said procedure of controlling comprises changing said atleast one parameter according to at least one of said depth of field,said specific environmental conditions said method is used in, saidmoving speed of said sensor, and characteristics of different objectsexpected to be found in said depth of field.
 45. The method according toclaim 43, wherein said procedure of controlling comprises thesub-procedures of providing said at least one energy pulse for aduration of said pulse width, delaying the opening of said sensor for aduration of said time said sensor is deactivated, T_(OFF), and receivingenergy pulses reflected from objects for a duration of said gating timespan said sensor is activated, T_(ON), and wherein said pulse width,said duration of said time said sensor is deactivated, T_(OFF), and saidgating time span said sensor is activated, T_(ON), define a cycle time.46. The method according to claim 45, wherein at least one repetition ofsaid cycle time forms part of an individual video frame, and a number ofsaid repetitions forms an exposure number for said video frame.
 47. Themethod according to claim 46, further comprising the procedure ofdynamically varying said exposure number by a control mechanism.
 48. Themethod according to claim 47, wherein said procedure of dynamicallyvarying comprises adjusting said exposure number according to a level ofambient light by said control mechanism.
 49. The method according toclaim 47, further comprising the procedure of intensifying saiddetection of said at least one reflection, and wherein said procedure ofdynamically varying comprises adjusting said exposure number by saidcontrol mechanism according to a level of current consumed by an imageintensifier utilized for said intensifying.
 50. The method according toclaim 47, further comprising the procedure of image processing bylocating areas in said sensor in a state of saturation by said controlmechanism.
 51. The method according to claim 47, further comprising theprocedure of image processing for a variable number of exposures by saidcontrol mechanism.
 52. The method according to claim 51, wherein saidprocedure of image processing comprises: taking at least two videoframes, one with a high exposure number, the other with a low exposurenumber, by image processing of a variable number of exposures;determining exposure numbers for said at least two video frames; andcombining frames to form a single video frame by combining dark areasfrom frames with a high exposure number and saturated areas from frameswith a low exposure number.
 53. The method according to claim 43,wherein said procedure of increasing is dynamic.
 54. The methodaccording to claim 43, wherein said pulse width and said gating timespan said sensor is activated, T_(ON), are limited to eliminate orreduce the sensitivity of said sensor to ambient light sources.
 55. Themethod according to claim 43, wherein said procedure of controllingcomprises shortening said pulse width progressively and lengthening saiddelay timing progressively, while retaining a cycle time of the saidgating unchanged.
 56. The method according to claim 43, wherein saidprocedure of controlling comprises shortening said gating time spanprogressively and lengthening said delay timing progressively, whileretaining a cycle time of said gating unchanged.
 57. The methodaccording to claim 43, wherein said procedure of controlling comprisesshortening said pulse width and said gating time span progressively,lengthening said delay timing progressively, while retaining a cycletime of said gating unchanged.
 58. The method according to claim 36,comprising calculating said energy pulse width, T_(LASER), substantiallydefined in accordance with the following equation:${2 \times \frac{R_{0} - R_{MIN}}{v}},$ where v is the speed said atleast one energy pulse travels at.
 59. The method according to claim 35,wherein said procedure of receiving comprises receiving several pulsesof said at least one energy pulse reflected from objects during a gatingtime span a sensor utilized for said receiving is activated, T_(ON). 60.The method according to claim 41, wherein said procedure of receivingcomprises receiving several pulses of said at least one energy pulsereflected from objects during a gating time span a sensor utilized forsaid receiving is activated, T_(ON); said procedure of gating comprisesa duration of time said sensor is deactivated, T_(OFF); and saidprocedure of controlling comprises controlling said gating time spansaid sensor is activated, T_(ON), and a duration of time said sensor isdeactivated, T_(OFF), substantially defined in accordance with thefollowing equations: $T_{ON} = {2 \times \frac{R_{0} - R_{MIN}}{v}}$ and${T_{OFF} = {\frac{2 \times R_{MIN}}{v} + T_{LASER}}},$ where R₀ is anoptimal range.
 61. The method according to claim 35, further comprisingthe procedure of intensifying said detection of said at least onereflection.
 62. The method according to claim 35, further comprising theprocedure of transmitting at least one image constructed from saidreceived at least one reflection.
 63. The method according to claim 35,further comprising the procedure of determining the level of ambientlight in said target area.
 64. The method according to claim 35, furthercomprising the procedure of determining if other energy pulses arepresent in said target area.
 65. The method according to claim 61,further comprising the procedure of overcoming glare from other energypulses by locally darkening the entrance of an image intensifierutilized for said intensifying.
 66. The method according to claim 35,wherein said procedure of emitting comprises emitting at least onepolarized electromagnetic pulse, and said procedure of receivingcomprises filtering received energy according to a polarizationconforming to an expected polarization of said at least one reflection.67. An imaging method, the method comprising the procedures of: emittingat least one energy pulse to a target area; receiving at least onereflection of said at least one energy pulse reflected from objectswithin a depth of a field to be imaged, characterized in that said depthof field having a minimal range, R_(MIN), said receiving comprisesgating detection of said at least one reflection such that said at leastone energy pulse is detected after a delay timing substantially given bythe time it takes said at least one energy pulse to reach said minimalrange and complete reflecting; and progressively increasing the receivedenergy of said at least one reflection reflected from objects locatedbeyond said minimal range along said depth of a field to be imaged, bycontrolling said at least one energy pulse and the timing of saidgating, said at least one energy pulse defines a substantial pulsewidth, T_(LASER), a pulse pattern, a pulse shape, and a pulse energy,said procedure of gating comprises a gating time span a sensor utilizedfor said receiving is activated, T_(ON), a duration of time said sensoris deactivated, T_(OFF), and a synchronization timing of said gatingwith respect to said at least one energy pulse, wherein a sensitivity ofa sensor utilized for said receiving relates to a gain andresponsiveness of said sensor in proportion to an amount of energyreceived by said sensor, wherein said gain received by said sensor as afunction of range R is defined by the follow convolution formula:${I_{r}(R)} = \frac{\int_{T_{LASER} + T_{OFF}}^{T_{LASER} + T_{OFF} + T_{ON}}{{{L\left( {t - \frac{2R}{v}} \right)} \cdot {C(t)}}{\mathbb{d}t}}}{T_{LASER}}$wherein L(t) defines a Boolean function representing an on/off status ofa transmission source utilized for said emitting, irrespective of astate of said sensor, wherein L(t)=1 if said transmission source is onand L(t)=0 if said transmission source is off, wherein C(t) defines aBoolean function representing an ability of said sensor to receiveincoming pulse reflections according to a state of said sensor, whereinC(t)=1 if said sensor is in an activated state and C(t)=0 if said sensoris in a deactivated state, and where v is the speed at which said atleast one energy pulse travels.
 68. The imaging method according toclaim 67, wherein a value for radiant intensity is obtained bymultiplying said convolution formula by a geometrical propagationattenuation function.